V.aTr.ut Aphides In California 
 
 By 
 .M. Davidson 

 
 / ' 
 
 UNIVERSITY OF CALIFORNIA 
 AT LOS ANGELES
 
 BULLETIN OF THE 
 
 No. 100 
 
 SB 
 
 Contribution from the Bureau of Entomology, L. O. Howard, Chief. 
 August 31, 1914. 
 
 (PROFESSIONAL PAPER.) 
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 By W. M. DAVIDSON, 
 
 Scientific Assistant, Deciduous Fruit Insect Investigations. 
 
 INTRODUCTION. 
 
 The study of walnut aphides dealt with in the following pages was 
 in early hi the year 1911 and continued until the summer of 1913. 
 
 ie observations were at first made at San Jose, CaL, but after Sep- 
 iber, 1912, the work was done chiefly at Walnut Creek, Cal. Prac- 
 
 5 ally all the life-history observations were made at the former 
 
 jality, and much of the control work was done at Walnut Creek. 
 
 ie habits of the aphides do not vary materially throughout Cali- 
 Drnia. It was at first the writer's intention to confine his studies to 
 ie European walnut aphis (OhromapJiis juglandicola Kalt.), as this 
 >ecies alone infests walnuts of commercial value grown in California, 
 
 it latterly two native species of Aphididae were found to be pests 
 
 . native walnuts much used for stock on which to graft the European 
 
 Persian nut, and thus the studies were extended so as to include 
 
 three species. The two native aphides above mentioned are Monellia 
 
 iryse Monell, .the American walnut aphis, which affects the eastern 
 
 lack walnut (Juglans nigra) and Monellia caryella Fitch, the little 
 
 ikory aphis, 1 which affects the California black walnut (Juglans 
 
 \ilifornica). Both of these species infest the Royal Hybrid walnut 
 
 cross between the eastern black walnut and the California black 
 
 ^alnut), while the Paradox Hybrid walnut (a cross between the 
 
 European walnut and the California black walnut) is attacked by the 
 
 European walnut aphis and to a lesser extent by the little hickory 
 
 )his. Both of these hybrids are rapid growers, and a certain per- 
 
 jntage of the seedlings obtained from the crossings makes good 
 
 >ck on which to graft the commercial varieties of nuts. The great 
 tajority of European nuts and their varieties are grown in California 
 
 I 1 This is the name Fitch gave to species which he found on hickory, and it seems best to retain it, 
 [though rather an unfortunate title in so far as California is concerned, as the only wild member of the 
 adace in that State is Juglans californica. 
 
 40859 Bull. 10014 1
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 on roots of either the California black walnut straight or on roots of 
 one or the other of these two hybrids. When a graft has been made 
 and both stock and scion are putting out leaves simultaneously, more 
 I than one species of aphis will usually occur on the same tree. In 
 such a case the two species feed on their own particular host, but the 
 migrant forms of either may bo found resting on foliage of the oppo- 
 site host. The Paradox and Royal hybrids are used in various parts 
 of California as shade trees and will furnish a fine grade of wood, 
 which will take on a high polish. 
 
 THE EUROPEAN WALNUT APHIS (Chromaphis juglandicola Kaltenbach). 
 
 Lachnus juglandicola Kaltenbach, Monographie der Familien der Pflanzenlause, 
 
 Aachen, 1843. 
 Callipterus juglandicola Koch, Die Pflanzenlause Aphiden, Nurnberg, p. 224, 
 
 1857. 
 
 Callipteras juglandicola Passerini, Gli Afidi, Parma, 1860. 
 Callipterus juglandis Walker, The Zoologist, ser. 2, v. 5, p. 2000, Feb., 1870. 
 Pterocallis juglandicola Buckton, Monograph of the British Aphides, v. 3, London, 
 
 1881, p. 32-34. 
 
 Callipterus juglandicola Schouteden, Mem. Soc. Ent. Belg., v. 12, p. 209-210. 
 Chromaphis juglandicola Essig, Mo. Bui. Cal. State Com. Hort., v. 1, no. 5, p. 
 
 190-194, figs. 72-73, April, 1912. 
 
 In 1870 Walker erected the genus ChromapJiis and designated 
 Callipterus juglandicola Kaltenbach as the type species. Reference 
 to this is made by H. F. Wilson in his paper "A Key to the Genera 
 and Notes on the Synonymy of the Tribe Callipterini, Family Aphi- 
 didae," Canad. Ent., v. 42, no. 8, p. 253-259, Aug., 1910. 
 
 HISTORY OF THE SPECIES. 
 
 The species was described originally by J. H. Kaltenbach in his 
 "Monographie der Familien der Pflanzenlause" as Lachnus juglandi- 
 cola. A somewhat free translation of this description is as follows : 
 
 Wingless: Pale yellow, egg-shaped, flat, square, incised, and armed with glandular 
 hairs on the margins; legs whitish- yellow, a black spot on the apex of the hind femora. 
 Length, \" '. 
 
 Winged: Yellow; eyes red; antenna) whitish, with black rings; cornicles yellow, 
 hardly noticeable; tail lacking. 
 
 This tree louse occurs sporadically in June and July in numbers under the leaves 
 of the walnut tree (Juglans regia). 
 
 Wingless: Antenna; shorter than the head and thorax combined, not markedly 
 jointed, whitish-yellow. Apex of antennae black, of third joint ringed black. Eyes 
 light red; beak short, scarcely reaching to the first coxae. On the dorsum occur two 
 longitudinal rows of black spots, which are absent on younger individuals. Cornicles 
 and tail lacking. Legs hyaline whitish-yellow; a black spot is found on the upper 
 side of the hind femora at their apices. 
 
 Winged: Antennae noticeably shorter than the body, pale, the four major joints 
 black at their apices; third joint distally enlarged; sixth joint with a gradually 
 tapering thin apex. The body is yellow; in many cases the black dorsal spots of the 
 abdomen are absent; .in other cases but two^to six are present; cornicles scarcely per-
 
 WALNUT APHIDES IN CALIFORNIA. 3 
 
 ceptible, yellow; tail not present. Legs pale; the spots on the apex of the hind 
 femora are larger than those of the wingless. In well-colored examples such spots 
 occur on the middle femora and those on the hind femora are enlarged into a ring. 
 The wings are transparent; the stigma yellow, cubitus and the two inner veins brown 
 and markedly stouter at the base, then gradually becoming finer and paler; veins of 
 lower wing and wing margin pale yellow; stigmatic or fourth vein very fine and 
 strongly curved. 
 
 There is no doubt that Kaltenbach's species is the same that 
 
 occurs commonly all over California on the European walnut. The 
 
 v^ black femoral spot, together with the antennse as described, estab- 
 
 \.^ lishes its identity. Kaltenbach's wingless form appears to be the 
 
 oviparous female in her penultimate molt, for the true apterous vivip- 
 
 s^arous female a common form in the majority of plant lice does 
 
 Qft not exist, or, if it does, is extremely rare, the author in two years of 
 
 close observation having failed to observe it. Buckton (1872) 1 
 
 i gives a description of the apterous viviparous form, but he also seems 
 
 ( v'to have had before him the immature oviparous form. 
 
 The bisect probably occurs wherever the European walnut is 
 grown. It has been reported from all over Europe, as well as from 
 the States of Colorado (Gillette, 1910), Oregon (Wilson and Lovett, 
 1911-12), and California (Essig, 1909). 
 
 GENERAL DESCRIPTION; CHARACTER AND EXTENT OF INJURY. 
 
 This aphidid is a small, lemon-yellow insect, about one-sixteenth 
 
 ~^of an inch in length. It occurs sporadically on the underside of the 
 
 leaves and on the young fruit of the European walnut (Juglans regia) 
 
 and its cultivated forms and hybrids. It appears on the upper sur- 
 
 \face of the leaf only at times of very severe infestation. It is to be 
 
 "'found from late February or early March until December, persisting 
 
 xas long as the leaves remain on the tree, but is present in greatest 
 
 ^numbers during the months of July and August. As many as 200 
 
 \ individuals may occur on a single large leaflet if infestation be severe, 
 
 o^ while the author has observed over 30 aphides on a single young nut. 
 
 Nuts badly infested while young never attain their normal size. 
 
 Many of them mature half-sized, covered on the upper surface with 
 
 the black sooty fungus which thrives on the sticky exudations of the 
 
 aphides. Attacks on the tree year by year also materially reduce 
 
 its vitality, since the aphides will be present in the spring even before 
 
 the leaves have opened and will remain until these drop. 
 
 Plate I, figure 1, shows the difference in size between infested and 
 uninfested nuts of one variety of European walnut, while Plate I, 
 figure 2, demonstrates the appearance of the sooty fungus on a 
 walnut leaf. 
 
 i Dates in parentheses refer to the Bibliography, p. 47. 
 
 242747
 
 BULLETIN 100, U. S. DEPARTMENT OF AGEICULTURE. 
 
 LIFE HISTORY AND TECHNICAL DESCRIPTIONS. 
 
 THE VIVIPAROUS OR ASEXUAL FORMS. 
 
 When the young stem-mother is ready to emerge in the spring she 
 causes the shell of the winter egg to burst with a longitudinal slit on 
 the dorsal surface from the micropylar end. (See fig. 1.) Egress is 
 performed head first, and antennae and legs are requisitioned by the 
 young larva in worming its way out of the shell. While the process 
 of emerging, which occupies half an hour or more, is taking place, the 
 aphis assumes an erect position at right angles to the long axis of the 
 egg. After the exit of the young the eggshell has a large triangular 
 hole at the micropylar end. 
 
 As soon as the buds begin to swell in early spring these stem-mothers 
 hatch and continue hatching until the leaves have fully opened out, at 
 which time all will have issued from the egg. The earliest plant-lice 
 to emerge may be seen wandering over the bare twigs and buds, 
 apparently feeding a little upon the scales protecting the unopened 
 buds, but not showing much growth until the buds 
 have opened and can afford nourishment. 
 
 Undoubtedly many of the aphides that hatch 
 early die of ill nourishment, and some of these do 
 not attain their full development for six or seven 
 weeks, while those hatching later and finding 
 tender food in abundance become full grown at 
 the end of five weeks - Certain it is that on a 
 times natural size. (Origi- particular tree the stem-mothers all became 
 winged almost simultaneously. On trees which 
 leaf early the stem-mothers will begin emerging [from the egg as 
 early as February 15, but on the Franquette and such late varie- 
 ties no aphides will be found until in April. Immediately after 
 hatching the lice seek the buds-or young leaves. In the former case 
 the aphides crawl in between the scales, but on the leaves they 
 appear on the lower or exposed side, notwithstanding the fact that 
 much better protection is afforded by the upper, as yet unfolded, sur- 
 face which at that time is almost entirely hidden from view. Possibly 
 the sticky character of the upper surface of the leaves repels them. 
 Table I indicates the life cycle of four stem-mothers which hatched 
 after the buds had opened. 
 
 TABLE 1. Period of development of the stem-mother of Chromaphis juglandicola, San 
 Jose, Cal., 1912. 
 
 No. of individual. 
 
 Date of 
 hatching. 
 
 Date of 
 acquiring 
 wings. 
 
 Period from 
 hatching to 
 maturity. 
 
 1.... 
 
 Mar. 24 
 
 Apr. 28 
 
 Day, 
 
 2 
 3 
 
 24 
 
 24 
 
 28 
 
 28 
 
 35 
 35 
 
 4 
 
 24 
 
 29 
 
 36 
 
 Average period. 
 
 
 
 35.25
 
 Bui. 100, U. S. Dept. of Agriculture. 
 
 PLATE I. 
 
 FIG. 1. THREE MATURED NUTS OF EUROPEAN WALNUT SEEDLING. 
 
 [Middle nut natural size, other two undersized from attack by aphides.] 
 
 FIG. 2. UPPER SIDE OF THREE LEAFLETS OF EUROPEAN WALNUT SEEDLING. 
 
 [The central leaflet shows growth of fungus thriving upon the exudation of aphides above. 
 Two-thirds natural size.]
 
 WALNUT APHIDES IN CALIFORNIA. 5 
 
 THE STEM-MOTHER; NEWLY HATCHED YOUNG (FIG. 2). 
 
 Oval, lemon yellow. Eyes red, of moderate size. Antennae 3-jointed, not quite 
 reaching to base of second coxae; joint III nearly three times as long as joints I and II 
 together. Legs comparatively long, entirely pale. Body covered with capitate 
 hairs. Cornicles very small, pale whitish-yellow, hardly raised above the surface of 
 the body. Cauda small, pale, bluntly conical. Beak entirely pale, reaching second 
 coxae. Black knee spots characteristic of this species absent. Measurements : Length 
 of body, 0.72 mm.; width, 0.30 mm.; antenna, joint I, 0.04 mm.; joint II, 0.035 mm.; 
 joint III, 0.145 mm. Almost immediately after birth the legs and antennae turn 
 dusky gray and the dark abdominal spots appear. In 
 this respect the young of the stem-mothers differ from 
 those of all other generations, for the appendages of the 
 young aphides of subsequent broods never turn entirely 
 dusky nor do the abdominal spots appear so early. 
 
 THE STEM-MOTHER; 4 DAYS OLD. 
 
 Yellowish-green, flatly oval, closely appressed to the 
 surface of the leaflet or bud scale. Antennae and legs 
 dusky gray. Eyes circular, red, small. Head, thorax, 
 two proximal antennal joints, and abdomen bearing capi- 
 tate hairs which arise (those of the antennae excepted) 
 from small tubercules situated in the middle of a small, FlG - 2.-cromopfci jug- 
 -.. i i i i . landicola: Stem-mother, newly 
 
 circular, dusky area. Antennae 3-jomted, the distal joint jacked (Original ) 
 the largest. Cornicles very small, erect. Cauda almost as 
 
 long as the hind tarsus, its apex blunt. Cornicles and cauda concolorous with the 
 abdomen. Beak very pale, reaching second coxae, its extreme apex brown. Under- 
 side of the head very pale yellow; of the abdomen greenish -yellow. 
 
 THE STEM-MOTHER; AFTER FIRST MOLT AND JUST PREVIOUS TO SECOND MOLT. 
 
 Pale lemon-yellow or yellowish green, flatly oval, closely appressed to the plant 
 surface, occurring on the underside of the expanding leaves, between the ribs. 
 Antennae and legs very pale yellow, almost hyaline. Antennae short, reaching slightly 
 beyond the posterior margin of the prothorax, 3-jointed, with a rudimentary suture 
 on the distal half of joint III . This joint is about three times as long as the two proxi- 
 mal joints together. Eyes crimson, not fully developed. Legs entirely pale, with- 
 out any trace of dark knee spots. Thorax and segments 1 to 6 of the abdomen with two 
 longitudinal rows of black or brown spots, on each of which occurs a small pale tubercle 
 bearing two capitate hairs, one larger than the other. On the thoracic segments and 
 on abdominal segments 1 to 7 occur two rows of pale lateral tubercles, each of which 
 bears three capitate hairs. The frontal margin of the head bears six such hairs on 
 tubercles. Antennal joints I and II with a capitate hair on their inner margins near 
 the middle, and joint III with one such hair on the inner margin near the base. The 
 eighth abdominal segment bears a dorsal fringe of six capitate hairs, those on either 
 end being smaller than the four inner ones. Cornicles situated on segment 6, as broad 
 as long, erect, concolorous with the abdomen. Cauda without armature, bluntly coni- 
 cal, almost hyaline, about as long as the hind tarsus. Beak barely reaching second 
 coxae , pale yellow, the extreme tip brown . Measurements : Length of body , 1 . 55 mm . ; 
 width, 0.775 mm.; antenna, joint I, 0. 053 mm.; joint II, 0:048 mm.; joint III, 0.304 
 mm. 
 
 Described from specimens collected at San Jose, Cal., March 28, 
 1912.
 
 6 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 After the second molt the spines on the dorsum of the body disap- 
 pear. (See fig. 3.) 
 
 The pupal and imaginal stages of the stem-mother show no appar- 
 ent difference in respect to size, color, or structure from those of the 
 
 later viviparous generations, and thus 
 one description of these forms will suf- 
 fice for all the winged viviparous gen- 
 erations. 
 
 THE PUPA OF THE WINGED VIVIPAROUS 
 FEMALE (FIG. 4). 
 
 General color pale lemon-yellow. Eyes red, 
 fully formed. Antennae reaching a little be- 
 yond the base of the wing-pads, pale, joint III 
 the longest, joints IV and V subequal. Ocelli 
 present. Anterior margin of the head bearing 
 six capitate spines. Thoracic segments pale 
 yellow. Wing-pads pale yellow, closely ap- 
 pressed to the sides of the body. Legs pale 
 FIG. 3. Chromaphis jv^landkola: Larva of yellow, with the dark knee spot on the hind 
 stem-mother after second molt. (Grig- fem0 ra only; tarsi dusky. Abdomen oval, pale 
 lemon-yellow, with a varying number of dark 
 
 spots on the dorsum, which spots are always present on segment 5 but often lacking on 
 the other segments. Head, thorax, and abdomen furnished with lateral rows of capi- 
 tate hairs which stand on small pale tubercles. Cornicles small, as wide aa long, 
 slightly constricted in the middle, situated on the sixth abdominal segment. Cauda 
 short, about as long as the cornicles, bluntly rounded at the apex. Cornicles and 
 cauda concolorous with the body. Beak short, pale, stout, reaching to the first pair of 
 coxae. The pupa has the legs relatively a little shorter than those of the adult and ia 
 thus more closely appressed to the leaf s tirf ace . The 
 body is quite flat. Measurements: Length of body, 
 1.87 mm. (average); width, 0.85 mm. (average max- 
 imum); antenna, joint I, 0.050 mm.; joint II, 
 0.042 mm.; joint III, 0.183 mm.; joint IV, 0.081 
 mm.; joint V, 0.076 mm.; joint VI, 0.065 mm.; 
 filament, 0.034 mm. Cornicles, 0.04 mm. 
 
 The stem-mothers pass through the 
 pupal molt about one week before the final 
 molt takes place, and after the latter they 
 acquire their full development as winged 
 adults. In the latter generations the 
 pupal instar occupies from three to six 
 days. 
 
 THE WINGED VIVIPAROUS FEMALE (FIG. 5). Fio. 4. Chromaphis juylandicola: 
 
 Pupa of winged viviparous fe- 
 
 General color pale lemon-yellow; many Individ- ma i e (Original ) 
 uals are darker yellow, yellowish-brown, or salmon- 
 pink. Antennae on very small frontal tubercles, about one-half the length 
 of the body, yellow, with the inner lateral margins of the first two joints dusky; 
 articulations of joints III to VI and the whole filament dusky to black. Eyes red. 
 Ocelli present. Prothorax yellow. Thoracic lobes and scutellum light brown, some- 
 times greenish-yellow, pale yellow in newly-molted individuals. Wings of medium
 
 WALNUT APHIDES IN CALIFORNIA. 7 
 
 size; subcosta and wing insertions pale yellow; stigma pale gray, with a darker area 
 at the confluence of the third discoidal vein, and another such though smaller area at 
 the apex; veins rather heavy, dark brown, all three discoidals arising from the sub- 
 costa and thickened at their bases; second branch of third discoidal nearer the wing 
 apex than the first fork; third discoidal describing a regular gentle curve for its entire 
 length; stigmatic vein entire, the depth of its curve varying in different examples, 
 generally reaching the wing margin midway between the apex of the stigma and the 
 the end of the third discoidal (often it touches the margin considerably nearer the 
 stigma, but rarely nearer the third discoidal) . Legs rather Aort, but a little longer than 
 those of the pupa; front pair yellow with the tarsi and apical third of the tibiae dusky 
 
 FIG. 5. Chromaphis juglandicola: Wingad viviparous female (appendages of left side removed), a, 
 Left antenna; 6, right cornicle; c, front tarsus. (Original.) 
 
 gray and the knee spot rarely present (gray when present); middle pair yellow, with 
 an indefinite gray spot on the upper side of the femur above the knee and with the 
 tarsi dusky gray; hind pair yellow, with a coal-black spot (sometimes produced into 
 an annulation) on the upper side of the femur above the knee joint and with the tarsi 
 dusky gray as in the other pairs. The knee spots are always present on the hind 
 femora, while they occur in about 80 per cent of individuals on the middle femora. 
 In 35 individuals examined throughout the year all had the spots on the hind femora, 
 28 had spots on the middle femora, and only 1 had spots on the fore femora. Abdomen 
 pale lemon-yellow, widest at segment 3, considerably wider than the thorax, gen- 
 erally bearing two oval brown spots on segment 5 and more rarely with two similar but 
 smaller spots onsegment4; occasionally immaculate. These spots are sometimes gray- 
 ish, varying in intensity, and appear to be the pupal markings retained in the adult form.
 
 8 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 Cornicles (fig. 5, 6) pale yellow, constricted in the middle, barely as long as broad. 
 Abdominal segments 3 to 6 inclusive bearing pale lateral tubercles. Body without 
 hairs. Cauda very pale, globular, about as long as the cornicles. Beak pale yellow, 
 the extreme tip black, reaching a little beyond the first coxae. Sternum pale brown. 
 Measurements: Length of body, 1.62-2.55 mm., average 2.08 mm.; width of body at 
 segment 3 of abdomen, 0.71-1.06 mm., average 0.88 mm.; wing expanse, 4.42-5.21 
 mm., average 4.77 mm.; antenna, joint I, 0.046-0.067 mm., average 0.055 mm.; joint 
 II, 0.039-0.055 mm., average 0.043 mm.; joint III, 0.267-0.408 mm., average 0.337 
 mm.; joint IV, 0.153-0.233 mm., average 0.196.mm.; joint V, 0.133-0.191 mm., aver- 
 age 0.162 mm.; joint VI, 0.079-0.094 mm., average 0.083 mm.; antennal filament, 
 0.038-0.043 mm., average 0.040 mm.; total length of antenna, 0.775-1.060 mm., aver- 
 age 0.916 mm.; cornicles, 0.05 mm.; cauda, 0.056 mm. 
 
 There are from 6 to 8 transverse oval sensoria on antennal joint III, 1 terminal sen- 
 sorium on joint V, and three terminal ones on joint VI. Buckton's measurements 
 (Buckton, 1872) seem to have been taken from small examples for, with the exception 
 of those of the antennal joints, his measurements are all smaller than the average found 
 by the writer. It may be that California examples are larger than the European. 
 
 Within a few hours after the last molt the wings harden and the chitin 
 stiffens. The stem-mothers then begin to deposit the young that 
 have been visible as pseudova for a week or longer inside their bodies. 
 In the life-history experiments the greatest number of young pro- 
 duced by one viviparous female was 44. These were extruded from 
 the body in 20 days, 30 in the first half and 14 in the last half of that 
 period. Several adults under observation deposited 11 or 12 young 
 within 12 hours after reaching maturity, and no more after that, 
 dying with many unborn pseudova in their bodies. In the field 
 the aphides deposit all their young on one leaf or on several leaves 
 near one another. The average number of young deposited by a single 
 adult ranges between 25 and 35. This seems to be about the same as 
 in other closely related Callipterini, but is a much smaller number 
 than that occurring in members of other tribes of Aphididse. The 
 aphides of the fall viviparous generation produce fewer young, 
 those which develop in November depositing only 6 or 8. As many 
 as 30 oval unborn aphides may be seen in the body of one recently 
 molted female. These embryos vary in size, only those to be de- 
 posited immediately being fully grown. Each is inclosed in a very 
 thin hyaline sac in which they are contained at birth. 
 
 The newly deposited young of the second and subsequent genera- 
 tions, both viviparous and oviparous, differ from the infant stem- 
 mothers in that they are entirely pale yellow (rarely suffused with a 
 faint pink) and remain thus until the first molt, while the young 
 stem-mothers have dusky appendages and abdominal spots. The 
 young deposited by the stem-mothers pass through their first molt 
 in from three to six days. After this molt there appear brown or 
 black dorsal spots in the majority of the individuals, and these 
 markings persist through the succeeding molts. A small percentage
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 9 
 
 of examples remain immaculate throughout development. The 
 "lice" of the second generation develop more quickly than the stem- 
 mothers or first generation, owing to greater abundance of food 
 supply and to the higher temperature existing at that later period. 
 In 1911 second-generation young were deposited in the field on 
 early varieties of walnuts a little before April 23, while in the following 
 year these were deposited as early as April 6. This is to be expected, 
 since in 1912 the trees came out in leaf two weeks earlier than in the 
 previous year. Table II shows the life cycle of 41 individuals of the 
 second generation at San Jose, Cal., in 1911. 
 
 TABLE II. Life cycle of the second generation of Chromaphis juglandicola, San Jose, 
 
 Cal., 1911. 
 
 
 Date of 
 
 
 
 Date of 
 
 
 No. of 
 individ- 
 ual. 
 
 
 Life 
 cycle. 
 
 No. of 
 individ- 
 ual. 
 
 
 Life 
 cycle. 
 
 Deposi- 
 tion. 
 
 Acquiring 
 wings. 
 
 Deposi- 
 tion. 
 
 Acquiring 
 wings. 
 
 1.... 
 
 Apr. 23 
 
 May 12 
 
 Days. 
 19 
 
 22 
 
 May 2 
 
 May 22 
 
 Days. 
 20 
 
 2 
 
 23 
 
 12 
 
 19 
 
 23 
 
 2 
 
 22 
 
 20 
 
 3 
 
 23 
 
 14 
 
 21 
 
 24 
 
 3 
 
 22 
 
 19 
 
 4 
 
 23 
 
 16 
 
 23 
 
 25 
 
 3 
 
 22 
 
 19 
 
 5 
 
 23 
 
 18 
 
 25 
 
 26 
 
 3 
 
 22 
 
 19 
 
 6 
 
 24 
 
 18 
 
 24 
 
 27 
 
 3 
 
 22 
 
 19 
 
 7 
 
 24 
 
 18 
 
 24 
 
 28 
 
 3 
 
 22 
 
 19 
 
 8 
 
 24 
 
 18 
 
 24 
 
 29 
 
 4 
 
 23 
 
 19 
 
 9 
 
 24 
 
 18 
 
 24 
 
 30 
 
 4 
 
 23 
 
 19- 
 
 10 
 
 24 
 
 18 
 
 24 
 
 31 
 
 5 
 
 25 
 
 20 
 
 11 
 
 25 
 
 20 
 
 25 
 
 32. .. . 
 
 5 
 
 25 
 
 20 
 
 12 
 
 28 
 
 21 
 
 25 
 
 33. .. . 
 
 5 
 
 25 
 
 20 
 
 13. . .. 
 
 May 1 
 
 21 
 
 20 
 
 34. -. . 
 
 6 
 
 26 
 
 20 
 
 14. . .. 
 
 1 
 
 21 
 
 20 
 
 
 6 
 
 26 
 
 20 
 
 15. . .. 
 
 1 
 
 21 
 
 20 
 
 se!!!! ! 
 
 6 
 
 27 
 
 21 
 
 16. . .. 
 
 1 
 
 21 
 
 20 
 
 37 
 
 6 
 
 27 
 
 21 
 
 17. - .. 
 
 1 
 
 21 
 
 20 
 
 
 6 
 
 27 
 
 21 
 
 18. . .. 
 
 2 
 
 21 
 
 19 
 
 39!!!! 
 
 7 
 
 27 
 
 20 
 
 19. . .. 
 
 2 
 
 21 
 
 19 
 
 40 
 
 8 
 
 28 
 
 20 
 
 20. . .. 
 
 2 
 
 22 
 
 20 
 
 41 
 
 9 
 
 27 
 
 18 
 
 21. . .. 
 
 2 
 
 22 
 
 20 
 
 
 
 
 
 Life cycle: 
 
 Maximum. . . 
 Minimum 
 Average 
 
 Days. 
 25 
 18 
 20.7 
 
 The aphides of the third generation appear on the earliest varieties 
 of walnuts about the middle of May, but on the late varieties such 
 as the Franquette this brood appears as much as a month later. The 
 individuals of this generation are on the average slightly larger than 
 those of other generations . In a large series of adult viviparous females 
 taken throughout the year of 1911 the largest example was of the third 
 generation. Its body was 2.55 mm. in length and 1.06 mm. in width, 
 and both of its antennae measured 1.06 mm., or 0.02 mm. in excess 
 of the next longest antenna in the series. Table III indicates the life 
 cycle of 97 individuals of the third generation. 
 40859 Bull. 10014 2
 
 10 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 TABLE III. Life cycle of the third generation of Chromaphis juglandicola, San Jose, 
 
 Cal, 1911. 
 
 
 Date of 
 
 
 
 Date of- 
 
 
 No. of 
 indi- 
 vidual. 
 
 Depo- 
 sition. 
 
 Acquir- 
 ing 
 
 wings. 
 
 Life 
 cycle. 
 
 No. of 
 indi- 
 vidual. 
 
 Depo- 
 sition. 
 
 Acquir- 
 ing, 
 wings. 
 
 Life 
 cycle. 
 
 1 
 
 May 19 
 
 June 
 
 Days. 
 16 
 
 50.... 
 
 May 19 
 
 June 7 
 
 Days. 
 19 
 
 2!".! 
 
 19 
 
 
 16 
 
 51 
 
 19 
 
 7 
 
 19 
 
 3 
 
 19 
 
 
 16 
 
 52 
 
 19 
 
 7 
 
 19 
 
 4 
 
 19 
 
 
 16 
 
 53 
 
 19 
 
 7 
 
 19 
 
 5 
 
 19 
 
 
 17 
 
 54 
 
 19 
 
 7 
 
 19 
 
 6 
 
 19 
 
 
 17 
 
 55 
 
 19 
 
 7 
 
 19 
 
 7 
 
 19 
 
 5 
 
 17 
 
 56 
 
 19 
 
 7 
 
 19 
 
 8 
 
 19 
 
 5 
 
 17 
 
 57 
 
 19 
 
 8 
 
 20 
 
 9 
 
 19 
 
 5 
 
 17 
 
 58 
 
 19 
 
 8 
 
 20 
 
 10 
 
 19 
 
 5 
 
 17 
 
 59 
 
 19 
 
 8 
 
 20 
 
 11 
 
 19 
 
 5 
 
 17 
 
 60 
 
 19 
 
 8 
 
 20 
 
 12 
 
 19 
 
 5 
 
 17 
 
 61 
 
 19 
 
 8 
 
 20 
 
 13 
 
 19 
 
 5 
 
 17 
 
 62 
 
 19 
 
 8 
 
 20 
 
 14 
 
 19 
 
 5 
 
 17 
 
 63 
 
 19 
 
 8 
 
 20 
 
 15 
 
 19 
 
 5 
 
 17 
 
 64 
 
 19 
 
 8 
 
 20 
 
 16 
 
 19 
 
 5 
 
 17 
 
 65 
 
 19 
 
 9 
 
 21 
 
 17 
 
 19 
 
 5 
 
 17 
 
 66 
 
 19 
 
 9 
 
 21 
 
 18 
 
 19 
 
 6 
 
 18 
 
 67 
 
 22 
 
 10 
 
 19 
 
 19 
 
 19 
 
 6 
 
 18 
 
 68 
 
 22 
 
 11 
 
 20 
 
 20 
 
 19 
 
 6 
 
 18 
 
 69 
 
 22 
 
 11 
 
 20 
 
 21 
 
 19 
 
 6 
 
 18 
 
 70 
 
 22 
 
 11 
 
 20 
 
 22 
 
 19 
 
 6 
 
 18 
 
 71 
 
 22 
 
 11 
 
 20 
 
 
 19 
 
 6 
 
 18 
 
 72 
 
 22 
 
 11 
 
 20 
 
 24!!!! 
 
 19 
 
 6 
 
 18 
 
 73 
 
 22 
 
 11 
 
 20 
 
 25 
 
 19 
 
 6 
 
 18 
 
 74 
 
 22 
 
 11 
 
 20 
 
 26 
 
 19 
 
 6 
 
 18 
 
 75 
 
 22 
 
 11 
 
 20 
 
 27 
 
 19 
 
 6 
 
 18 
 
 76 
 
 22 
 
 11 
 
 20 
 
 28 
 
 19 
 
 6 
 
 18 
 
 77 
 
 22 
 
 11 
 
 20 
 
 .29 
 
 19 
 
 6 
 
 18 
 
 78 
 
 22 
 
 11 
 
 20 
 
 30 
 
 19 
 
 6 
 
 18 
 
 79 
 
 22 
 
 11 
 
 20 
 
 31 
 
 19 
 
 6 
 
 18 
 
 80 
 
 22 
 
 11 
 
 20 
 
 32 
 
 19 
 
 6 
 
 18 
 
 81 
 
 22 
 
 11 
 
 20 
 
 33 
 
 19 
 
 6 
 
 18 
 
 82 
 
 22 
 
 11 
 
 20 
 
 34 
 
 19 
 
 6 
 
 18 
 
 83 
 
 22 
 
 11 
 
 20 
 
 35 
 
 19 
 
 6 
 
 18 
 
 84 
 
 22 
 
 12 
 
 21 
 
 36 
 
 19 
 
 6 
 
 18 
 
 85 
 
 22 
 
 12 
 
 21 
 
 37 
 
 19 
 
 6 
 
 18 
 
 86 
 
 22 
 
 12 
 
 21 
 
 38 
 
 19 
 
 6 
 
 18 
 
 87 
 
 22 
 
 12 
 
 21 
 
 39 
 
 19 
 
 6 
 
 18 
 
 88 
 
 22 
 
 12 
 
 21 
 
 40 
 
 19 
 
 6 
 
 18 
 
 89 
 
 22 
 
 12 
 
 21 
 
 41 
 
 19 
 
 6 
 
 18 
 
 90 
 
 22 
 
 13 
 
 22 
 
 42 
 
 19 
 
 6 
 
 18 
 
 91 
 
 22 
 
 13 
 
 22 
 
 43 
 
 19 
 
 7 
 
 19 
 
 92 
 
 22 
 
 13 
 
 22 
 
 44 
 
 19 
 
 7 
 
 19 
 
 93 
 
 22 
 
 14 
 
 23 
 
 45 
 
 19 
 
 7 
 
 19 
 
 94 
 
 22 
 
 14 
 
 23 
 
 46 
 
 19 
 
 7 
 
 19 
 
 95 
 
 22 
 
 14 
 
 23 
 
 47 
 
 19 
 
 7 
 
 19 
 
 96 
 
 22 
 
 15 
 
 24 
 
 48 
 
 19 
 
 7 
 
 19 
 
 97 
 
 22 
 
 15 
 
 24 
 
 49 
 
 19 
 
 7 
 
 19 
 
 
 
 
 
 Life cycle: Days. 
 
 Maximum 24 
 
 Minimum 16 
 
 Average 19. 1 
 
 Generations IV to VIII inclusive occupy roughly 16 days apiece 
 for development, and this period is the average life cycle during the 
 summer months. Some aphides will develop in 14 days and others 
 in 19 or 20. Table IV gives the life-cycle records of these five genera- 
 tions and also that of the ninth. The records hi some instances are 
 small, but the fact that in the first five of these generations there is 
 practically no difference in the duration of the life cycle was cor- 
 roborated by a larger series of experiments during the summer months 
 with individuals of which the respective generations were unknown.
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 11 
 
 TABLE IV. Life cycle of the summer generations of Chromaphis juglandicola, San Jose 
 
 Cal, 1911. 
 
 
 
 Date of 
 
 
 
 Generation No. 
 
 No. indi- 
 vidual. 
 
 Deposi- 
 tion. 
 
 Reach- 
 ing adult 
 state. 
 
 Life 
 
 cycle. 
 
 Form of indi- 
 vidual. 
 
 
 
 
 
 Day.". 
 
 
 
 1 
 
 June 8 
 
 June 28 
 
 20 
 
 Viviparous. 
 
 
 2 
 
 16 
 
 July 1 
 
 15 
 
 60. 
 
 
 3 
 
 16 
 
 1 
 
 15 
 
 Do. 
 
 IV 
 
 4 
 
 16 
 
 1 
 
 15 
 
 Do. 
 
 
 5 
 
 16 
 
 2 
 
 16 
 
 Do. 
 
 
 6 
 
 16 
 
 2 
 
 16 
 
 Do. 
 
 
 7 
 
 16 
 
 2 
 
 16 
 
 Do. 
 
 
 1 
 
 July 1 
 
 15 
 
 14 
 
 Do. 
 
 V 
 
 2 
 
 j 
 
 15 
 
 14 
 
 Do. 
 
 
 3 
 
 1 
 
 17 
 
 16 
 
 Do. 
 
 
 4 
 
 1 
 
 18 
 
 17 
 
 Do. 
 
 
 1 
 
 15 
 
 31 
 
 16 
 
 Do. 
 
 
 2 
 
 15 
 
 31 
 
 16 
 
 Do. 
 
 
 3 
 
 15 
 
 31 
 
 16 
 
 Do. 
 
 
 4 
 
 15 
 
 31 
 
 Id 
 
 Do. 
 
 
 5 
 
 15 
 
 31 
 
 16 
 
 Do. 
 
 
 6 
 
 15 
 
 31 
 
 16 
 
 Do. 
 
 
 7 
 
 15 
 
 31 
 
 16 
 
 Do. 
 
 
 8 
 
 16 
 
 Aug. 1 
 
 16 
 
 Do. 
 
 
 9 
 
 16 
 
 1 
 
 16 
 
 Do. 
 
 
 10 
 
 16 
 
 1 
 
 16 
 
 Do. 
 
 VI 
 
 11 
 
 16 
 
 2 
 
 17 
 
 Do. 
 
 
 12 
 
 16 
 
 2 
 
 17 
 
 Do. 
 
 
 13 
 
 16 
 
 2 
 
 17 
 
 Do. 
 
 
 14 
 
 16 
 
 2 
 
 17 
 
 Do. 
 
 
 15 
 
 17 
 
 2 
 
 16 
 
 Do. 
 
 
 16 
 
 17 
 
 2 
 
 16 
 
 Do. 
 
 
 17 
 
 17 
 
 2 
 
 16 
 
 Do. 
 
 
 18 
 
 17 
 
 3 
 
 17 
 
 Do. 
 
 
 19 
 
 17 
 
 4 
 
 18 
 
 Do. 
 
 
 20 
 
 18 
 
 5 
 
 18 
 
 Do. 
 
 
 21 
 
 18 
 
 6 
 
 19 
 
 Do. 
 
 
 22 
 
 18 
 
 6 
 
 19 
 
 Do. 
 
 
 1 
 2 
 
 Aug. 2 
 
 17 
 
 17 
 
 15 
 15 
 
 Do. 
 Do. 
 
 VII 
 
 3 
 
 2 
 
 17 
 
 15 
 
 Do. 
 
 
 4 
 5 
 
 2 
 3 
 
 19 
 20 
 
 17 
 17 
 
 Do. 
 Do. 
 
 
 6 
 
 3 
 
 20 
 
 17 
 
 Do. 
 
 
 7 
 
 3 
 
 20 
 
 17 
 
 Do. 
 
 
 1 
 
 2 
 
 IS 
 19 
 
 Sept. 1 
 
 14 
 14 
 
 Do. 
 Oviparous. 
 
 
 3 
 
 19 
 
 2 
 
 14 
 
 t>0. 
 
 
 4 
 
 19 
 
 3 
 
 15 
 
 Do. 
 
 
 5 
 
 19 
 
 3 
 
 15 
 
 Do. 
 
 
 6 
 
 19 
 
 3 
 
 15 
 
 Do. 
 
 
 7 
 
 19 
 
 3 
 
 15 
 
 Do. 
 
 
 8 
 
 19 
 
 3 
 
 15 
 
 Do. 
 
 VIII 
 
 9 
 
 19 
 
 3 
 
 15 
 
 Do. 
 
 
 10 
 
 20 
 
 4 
 
 15 
 
 Do. 
 
 
 11 
 
 20 
 
 4 
 
 15 
 
 Do. 
 
 
 12 
 
 20 
 
 4 
 
 15 
 
 Do. 
 
 
 13 
 
 20 
 
 6 
 
 17 
 
 Viviparous. 
 
 
 14 
 
 20 
 
 6 
 
 17 
 
 Oviparous. 
 
 
 15 
 
 20 
 
 6 
 
 17 
 
 So. 
 
 
 16 
 1 
 
 20 
 
 Sept. 5 
 
 7 
 30 
 
 18 
 25 
 
 Viviparous. 
 Oviparous. 
 
 
 2 
 
 5 
 
 Oct. 1 
 
 26 
 
 So. 
 
 
 3 
 
 5 
 
 6 
 
 31 
 
 Viviparous. 
 
 
 4 
 
 5 
 
 6 
 
 31 
 
 60. 
 
 
 5 
 
 5 
 
 8 
 
 33 
 
 Do. 
 
 
 6 
 
 5 
 
 8 
 
 33 
 
 Do. 
 
 
 7 
 
 7 
 
 9 
 
 32 
 
 Do. 
 
 IX 
 
 8 
 
 7 
 
 11 
 
 34 
 
 Do. 
 
 
 9 
 
 7 
 
 13 
 
 36 
 
 Do. 
 
 
 10 
 
 7 
 
 14 
 
 37 
 
 Do. 
 
 
 11 
 
 7 
 
 14 
 
 37 
 
 Do. 
 
 
 12 
 
 8 
 
 12 
 
 34 
 
 Do. 
 
 
 13 
 
 8 
 
 17 
 
 39 
 
 Do. 
 
 
 14 
 
 8 
 
 17 
 
 39 
 
 Do.
 
 12 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 An inspection of Table IV shows that the length of the life cycle 
 of Generations IV to VII was almost the same. This is to be ex- 
 pected, since in 1911 the months of June, July, and August had 
 almost identical temperatures both day and night. It will also be 
 observed that there was a very noticeable difference between the life- 
 cycle periods of Generations VIII and IX, 16 individuals of the eighth 
 generation averaging 15.4 days and 14 individuals of the ninth gen- 
 eration averaging 33.4 days. The ninth generation thus required 
 for development a period over twice as long as that required by the 
 preceding generation, developing almost as slowly as the stem 
 mother generation (see Table I). Yet the temperature during the 
 daytime influencing the ninth generation differed but little from 
 those which obtained during the development of the eighth. The 
 probable causes of the slow development of the ninth generation lice 
 is to be found in the colder night temperatures to which they were 
 subjected and in the fact that the leaves at this time are becoming 
 less vigorous and consequently afford poorer nourishment for the 
 aphides than earlier in the season. There is a tenth generation, and 
 in warm early seasons probably an eleventh, but in these generations 
 the brood is small and the "lice" grow slowly. Plant lice may be 
 found in early December giving birth to young, which are destined 
 to perish either when the leaves drop or through exposure to hard 
 frost. The author has observed dead aphides of all sizes on the 
 brown frosted leaves during early winter. 
 
 All the plant lice used for the life-history experiments were reared 
 out of doors on young seedling walnut trees planted in pots and in- 
 closed with glass cylinders. In 1911 the stock was procured from 
 stem mothers collected on the earliest varieties of walnuts. When 
 the work was started in 1911 it was too late to procure eggs, and so 
 the data on the stem-mother cycle was acquired in 1912. 
 
 After the ninth generation no more life-history experiments were 
 carried on in the rearing cages, but a weekly examination was made 
 of infested leaves in the field to determine the proportions of tho dif- 
 ferent forms, sexual and asexual, during the fall months. 
 
 THE OVIPAROUS OR SEXUAL FORMS. 
 
 The oviparous forms are the true sexes, comprising the winged 
 male and the wingless oviparous, or egg-producing, female. The 
 female aphis, after fertilization by the male, deposits true eggs, in 
 which form alone the insect can tide over the winter months when 
 no food supply is procurable. 
 
 As is shown in Table IV, there is no real oviparous generation, for 
 in all the later or fall generations a certain percentage of the young 
 will develop either into the sexed males or the sexed females. On 
 heavily infested trees oviparous aphides appear as early in the season
 
 WALNUT APHIDES IN CALIFOENIA. 
 
 13 
 
 as July, while on trees attacked by few lice these forms will not occur 
 until September or October. It therefore seems that the more 
 heavily a tree is infested the earlier will the sexed forms be produced. 
 A glance at Table IV demonstrates that the first oviparous form 
 of the life-cycle material became adult September 2, and was a 
 member of the eighth generation. In the field the first oviparous 
 form was observed in 1911 on July 7, and in 1912 on July 9. Both of 
 these occurred on early-leafing trees and probably belonged to the fifth 
 or sixth generation. As the growth of the aphis colony may be said to 
 have reached its zenith about the middle of July, it is at the time of 
 its greatest abundance that the sexed individuals begin to appear. 
 And, indeed, for the welfare of the species they appear none too 
 soon, for it is in July and August that the hordes of natural enemies 
 work tremendous havoc, frequently cleaning up a bad infestation on 
 a tree within three weeks. Those sexual females that have gone to 
 the trunk and limbs to deposit their eggs very often escape destruc- 
 tion while the others remaining on the foliage are devoured. Until 
 the middle of August the sexual forms are comparatively rare and 
 comprise less than 5 per cent of the whole, but after that time they 
 become more and more abundant. The sexed females always greatly 
 outnumber the males. Table V indicates the advance and decline 
 of the sexual forms in the late summer and fall. The data were ob- 
 tained by weekly visits to badly infested trees, during which the 
 lice on a certain number (50) of leaflets picked out at random were 
 counted. It must be borne in mind that as the fall advances more 
 and more sexual females repair to the limbs for the purpose of depos- 
 iting their eggs, and that therefore in the case of the later counts a 
 really greater proportion of these were present on the trees than 
 would appear from the records. 
 
 TABLE V. Comparative numbers of sexual and asexual forms of Chromaphisjuglandicola 
 observed on the foliage at different dates, San Jose, CaL, 1911. 
 
 Date of collection. 
 
 Number of 
 
 Percent- 
 age of 
 
 Vivipa- 
 rous 
 forms. 
 
 Ovipa- 
 rous 
 forms. 
 
 Males. 
 
 Vivipa- 
 rous 
 forms. 
 
 September 15 ... 
 
 241 
 258 
 203 
 171 
 166 
 207 
 172 
 420 
 233 
 10 
 
 247 
 355 
 H3 
 66 
 74 
 117 
 111 
 80 
 36 
 
 
 4 
 5 
 6 
 9 
 14 
 9 
 4 
 11 
 
 
 
 49 
 42 
 58 
 70 
 65 
 02 
 60 
 82 
 84 
 100 
 
 23 
 
 30 
 
 October 7 
 
 14.. 
 
 
 g 
 
 16 
 
 23 
 
 Total 
 
 2,081 
 
 1,229 
 
 69 
 
 ""ei.'e 
 
 
 
 

 
 14 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 The maximum number of aphides found on a single leaflet through- 
 out the counts was 90, of which 64 were sexual females. This oc- 
 curred on the first date of collection. 
 
 It will be noticed from Table V that on the first two dates the ovi- 
 parous forms were predominant but that on all later dates these were 
 outnumbered by the viviparous individuals. On the date of the 
 fourth collection (October 7) numerous sexual females were found on 
 the limbs of the tree, and their number was more and more augmented 
 each succeeding week. About October 1 the males appeared in num- 
 bers, very few of them having been in evidence previous to this time, 
 although the first male of the season was noticed July 10. Table VI 
 indicates the preponderance in numbers of the sexual female over 
 the male. 
 
 TABLE VI. Preponderance of the sexual female of Chromaphis juglandicolaover themale. 
 
 Date of collection or count. 
 
 Number of 
 sexual 
 females to 
 each male. 
 
 Date of collection or count. 
 
 Number of 
 sexual 
 females to 
 each male. 
 
 September 15 
 
 62 
 
 October 24 
 
 13 
 
 
 71 
 
 November 2 
 
 28 
 
 30 
 
 24 
 
 9 
 
 
 October 7 
 
 7.3 
 
 16 
 
 5 
 
 14 
 
 5.3 
 
 23... 
 
 (i) 
 
 
 
 
 
 i None of either sex seen on leaves. 
 
 Table VI was compiled from the same material as that used for 
 Table V. On November 9 nearly all the sexual females were clus- 
 tered on the limbs, and two weeks later they and all other plant lice 
 at the experimental trees succumbed to a severe frost, which had 
 at the same time withered all the leaves. This clustering of the 
 sexual females or sexuparse about the limbs explains the small per- 
 centage of this form as compared with the males on November 9 
 and 16. 
 
 Copulation seems to occur only on the leaf, and the females are not 
 fertilized until they have passed through the last molt. A single 
 male may fertilize several females probably quite a large number 
 when it is considered that the latter sex so greatly outnumbers the 
 former and that very few eggs prove infertile. Copulation in all 
 instances observed by the writer occupied some 30 seconds of time 
 a very short p^iod for an aphis. If the male be disturbed, he will 
 immediately retract his genital organ and move off. In 1912 the 
 males appeared in comparative abundance in the vicinity of San 
 Jose as early as August 26. 
 
 In general appearance the adult oviparous female differs from the 
 viviparous form in that it is wingless, has a wider body, and bears 
 three conspicuous transverse brown or black bands on the dorsum 
 of the abdomen. The male is greenish-yellow, winged, with black
 
 WALNUt APHIDES IN CALIFORNIA. 
 
 15 
 
 Or dusky gray legs and antennae. The oviparous or sexual female 
 molts four times but does not differ in appearance from the viviparous 
 form until the third molt is 
 
 FIG. 6. Ckromaphis juglandicola: Oviparous 
 female, penultimate instar. (Original.) 
 
 THE OVIPAROUS FEMALE, AFTER THE THIRD MOLT (FIG. 6)< 
 
 Rather smaller and narrower than the full-grown form. General color pale gamboge* 
 
 yellow, sometimes lemon yellow. Body twice 
 
 as long as wide. Eyes bright red. Head with 
 
 six erect, capitate spines on the anterior margin. 
 
 Antennae short, reaching barely to the middle of 
 
 the mesothorax; 7-jointed, joint III the longest, 
 
 joints IV and V subequal, joint VI longer than 
 
 its spur or filament. Spur dusky, rest of anten- 
 nae pale lemon yellow. Head, thorax, and ab- 
 domen with two longitudinal rows of oval black 
 
 spots on the dorsum. Thorax and abdominal 
 
 segments 1-5 with two lateral longitudinal rows 
 
 of circular black spots, on which are situated 
 
 small tubercles bearing capitate hairs. Such 
 
 tubercles also occur on the black dorsal spots. 
 
 Eighth segment of the abdomen unmarked, 
 
 bearing on its posterior margin a fringe of six 
 
 capitate hairs. Legs pale greenish-yellow with 
 
 the characteristic knee spot on the hind femora 
 
 only; tarsi gray. Cornicles on the sixth segment, quite small, wider than long, pale 
 
 lemon-yellow. Cauda equal in length to the hind tarsus, pale yellow, rounded. Beak 
 
 very pale, almost white, reaching to the anterior coxae. Measurements: Length of 
 
 body, 1.51 mm.; width of body, 0.76 
 mm.; antennae, joint I, 0.063 mm.; 
 joint II, 0.048 mm.; joint III, 0.136 
 mm.; joint IV, 0.083 mm.; joint V, 
 0.085 mm. ; joint VI, 0.086 mm. ; fila- 
 ment, 0.021 mm. 
 
 Described from specimens 
 collected at Walnut Creek, CaJ., 
 and San Jose, Cal., October 16 
 to 26, 1912. 
 
 THE OVIPAROUS FEMALE, ADULT STAGE 
 (FIG. 7). 
 
 General color gamboge, varying in 
 newly molted examples to lemon yel- 
 low and in older individuals to salmon 
 pink or with a distinct brownish tint. 
 Eyes crimson. Head and prothorax 
 with indefinite dusky brown markings. 
 Ocular tubercles small. Anterior mar- 
 gin of the head with six capitate hairs 
 projecting forward. Thorax mottled all over with shades of brown, its lateral margins 
 lighter. Prothorax with two capitate hairs on either side of its posterior portion. Ab- 
 domen with two or three hairs on the lateral margins of each segment. Segments 4 and 
 5 and posterior half of 3 with dark brown or black markings which generally coalesce to 
 
 - Chromaphis juglandicola: Oviparous female. 
 Right antenna. (Original.)
 
 16 BULLETIN 100, U. S. DEPARTMENT OP AGRICULTURE. 
 
 form three transverse bars or bands, of which those on segments 4 and 5 do not quite reach 
 the lateral margins of the segments, while that on the third segment is slightly shorter 
 and but half as broad as the others. Wings absent. Cornicles quite similar to those of 
 the winged viviparous female. Cauda globular, concolorous with the abdomen, larger 
 than that of the winged viviparous female. Anal plate large, U-shaped, extending 
 beyond the cauda when viewed from above. In reality it has a shallow incision at 
 the apex. Antennae on slight frontal tubercles, reaching to the middle of the meta- 
 thoracic segment, white, with the apices of joints 3 to 6 black. Legs very pale yellow, 
 almost hyaline; tarsi dusky gray at their apices. All six femora have the character- 
 istic black or brown knee spot. Beak yellow, the extreme tip black, reaching to the 
 second coxae. Hind tibiae not much swollen, bearing about 35 circular sensoria 
 occurring evenly on the middle two-thirds of the tibia and arranged in an irregular 
 Bpiral. Measurements: Length of body, 1.60 mm.; width of body, 0.81 mm.; an- 
 tenna, joint I, 0.06 mm.; joint II, 0.04 mm.; joint III, 0.22 mm.; joint IV, 0.125 
 mm.; joint V, 0.109 mm.; joint VI, 0. 081 mm.; filament, 0.023 mm. Cornicles, 0.06 
 mm. Cauda, 0.085 mm. 
 
 Described from specimens collected in the fall of 1911 at San 
 Jose, Cal. 
 
 THE FULL-GROWN MALE PUPA. 
 
 In its immature stages the male pupa resembles the oviparous 
 female. A description of a single full-grown male pupa taken at 
 San Jose, Cal., October 27, 1912, is as follows: 
 
 General color pale lemon yellow. Antennae pale, whitish, i caching to the anterior 
 margin of the metathorax; last three joints black or dusky. Head and prothorax 
 brownish. Eyes bright red. Wing pads very pale. Legs entirely whitish, only the 
 hind femora bearing the characteristic knee spot; tarsi dusky gray. Cornicles as 
 broad as long. Cauda very small, rounded. Cornicles and cauda pale yellow. Head, 
 thorax, and abdomen with two longitudinal dorsal rows of oval black spots and with 
 two such lateral rows of circular black spots. On each of these spots is situated a tuber- 
 cle having a single capitate hair. Excluding the wing pads the body resembles that 
 of the immature sexual female. Measurements: Length of body, 1.01 mm.; width 
 of body, 0.50 mm.; antenna, joint I, 0.049 mm.; joint II, 0.035 mm.; joint III, 
 0.121 mm.; joint IV, 0.081 mm.; joint V, 0.087 mm.; joint VI, 0.063 mm.; filament, 
 0.023 mm. 
 
 THE WINGED MALE, ADULT STAGE (FIG. 8). 
 
 General color of the body pale yellow or greenish yellow. Head, prothorax, and 
 thorax grayish black. Scutellum black. Eyes bright red. Antennae not on frontal 
 tubercles, reaching to the posterior margin of the first abdominal segment, pale yellow; 
 joints I and II, the filament or spur, and the articulations of joints III to VI dusky 
 gray. These dark articular annulations are less pronounced than in the viviparous 
 female. Wings of medium size; costa, subcosta, and insertions pale yellowish gray; 
 stigma short and gray, with its central area paler; veins gray, second fork of third 
 discoidal nearer to the wing apex than to the first fork and arising beyond the apex 
 of the stigmatic vein; stigmatic vein evenly and gently curved, absent in the middle 
 for a space equal to one-third of its length. Legs longer in proportion to the body than 
 those of the other forms; front legs and middle tibiae very pale yellow or yellowish 
 green; distal two- thirds of the middle and hind femora shaded gray, the black knee 
 spot being present on these four femora; hind tibiae shaded gr&y for its proximal three- 
 fourths, its apical fourth pale yellow; all tarsi light gray. Abdomen barely as long 
 as the head and thorax combined, widest at the fourth segment, and with a pair of
 
 Bui. 100, U. S. Dept. of Agricultu 
 
 PLATE II. 
 
 EGGS OF EUROPEAN WALNUT APHIS (CHROMAPHIS JUGLANDICOLA) ON 
 PIECE OF BARK OF EUROPEAN SEEDLING WALNUT. TWICE NATURAL 
 SIZE.
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 17 
 
 oval gray transverse spots on the fifth segment, which are separated by a space equal 
 to their length. Cornicles pale yellow, about as broad at the base as long, very much 
 as in the winged female. Cauda pale yellow, globular, not quite as long as the hind 
 tarsus. Sexual organ pale yellow. Beak pale yellow, slightly exceeding the fore 
 coxse. Sterna black. Sensoria transversely oval, situated in an irregular row aa 
 follows; joint III, 11 to 16; joint IV, 5 to 7; joint V, 4 to 5; joint VI, 2 besides usual 
 terminal. 
 
 Measurements: Length of body (average), 1.47 mm.; width of body (maximum), 
 Q.48 mm.; expanse of wings (average), 4.20 mm; antenna, joint I, 0.05 mm.; joint II, 
 0.04 mm.; joint III, 0.34 mm.; joint IV, 0.12 mm.; joint V, 0.12 mm.; joint VI, 0.08 
 mm. ; filament, 0.03 mm. ; cornicles, 0.05 mm. 
 
 a-pMs juglandicola: Winged male (appendages of left side removed), a, Left antenna. 
 (Original.) 
 
 Described from many individuals collected in 1911 and V12 at 
 San Jose, Cal. 
 
 Both the male and the winged viviparous female .nen disturbed 
 have a habit if jumping psyllid-like into the air. Their flight is 
 generally in the form of a long spiral, and when disturbed they fly in 
 an upward direction. 
 
 EGG DEPOSITION. 
 
 As mentioned before, the first sexual females of the year remain 
 longer on the leaves after they have reached the adult state than 
 those developing later. In 1911 eggs were not observed in the 
 field until September, or seven weeks after the first appearance of 
 sexual females. In 1912 some eggs appeared in August. This long 
 period between the first appearance of the sexed females and the 
 40859 Bull. 10014 3
 
 18 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 earliest egg deposition may be explained by the fact that until late 
 in August males are quite scarce and so the females must wait on 
 the leaves until the males are developed. Directly after mating the 
 female repairs to the branches and limbs to deposit her eggs. Al- 
 though eggs may be deposited anywhere along the limbs, and more 
 rarely on the newer growth, the locations most preferred are the old 
 scars of fallen leaves and the surface of the larger limbs near their 
 bases. Another favored location is that in the crotches of the smaller 
 limbs. Eggs are rarely laid along the stalk of the leaf or at the base 
 of the leaflets, and if placed in those positions they fall to the ground 
 when the leaf drops. Cavities and interstices in the bark are also 
 chosen, but when infestation is very severe the eggs are laid in the 
 open on the larger limbs (see PL II). In such a case large groups of 
 eggs are massed together by many females, but a single female lays not 
 more than three or four in a group. The eggs are fastened together 
 and to the plant surface by a thin, transparent, gluey substance. No 
 accurate information was obtained as to the number of eggs a single 
 aphis produced, but from general field observations together with 
 dissections of gravid females the writer arrived at the conclusion that 
 not more than 30 eggs fell to the share of each adult, and probably 
 not over half that number. On July 20, 1911, five gravid females 
 were dissected. These contained respectively 5, 3, 3, 4, and 4 well- 
 developed ova, besides about a dozen much smaller ones. On August 
 28, 1912, four oviparous females dissected contained respectively 
 2, 2, 4, and 2 full-grown ova besides about 20 much smaller ones. All 
 these individuals were taken on the leaves and had not oviposited. 
 The largest eggs dissected were lozenge-shaped and measured 0.37 
 mm. in length by 0.14 mm. in width. 
 
 THE EGG (FIG. l; PL. n). 
 
 When first laid, the egg is pale lemon-yellow or whitish yellow, oval, 
 almost twice as long as broad, flatter than most eggs of Aphidida?, 
 and slightly broader at the micropylar end. After two or three days 
 it turns black and shines obscurely when placed under a strong light. 
 The surface is beautifully sculptured with granular hexagonal mark- 
 ings. These markings arc thickened portions of the shell. The nar- 
 row intermediate portions of the shell are extremely thin, so much so 
 that four months after the egg has been laid the yellow interior sub- 
 stance is plainly visible through them if subjected to a high power of 
 magnification. It appears that about 85 per cent of the eggs are 
 fertile. The average size is 0.50 mm. by 0.28 mm. The egg stage 
 may be said to occupy, on the average, five months in California.
 
 WALNUT APHIDES IN CALIFORNIA. 19 
 
 ANT ATTENDANTS. 
 
 The sweet juices excreted by the European walnut aphis attract 
 large numbers of ants, of which a large black species, Formica sub- 
 sericea Say, is the most abundant. The author is indebted to Mr. 
 Theo. Pergande, of the Bureau of Entomology, Washington, D. C., 
 for the determination of this species. 
 
 THE AMERICAN WALNUT APHIS (Monellia caryae Monell). 1 
 
 Callipterus 2 caryae Monell, U. S. Geol. & Geog. Survey Bui. 5, No. 1, p. 31, Jan. 22, 
 1879. 
 
 Monellia 3 caryae Gillette, Jour. Econ. Ent., v. 3, No. 4, p. 367, fig. 6, Aug., 1910. 
 
 HISTORY OF THE SPECIES. 
 
 This plant-louse was first collected in Missouri by Mr. J. T. Monell 
 in 1879. His original description is as follows: 
 
 Winged form; general color pale yellow; tips of antennal joints black; legs entirely 
 pale whitish. Antennae a little shorter than the body; seventh joint equal to or 
 one-third longer than the preceding; fifth joint as long as the two following taken 
 together. Nectaries not perceptible. Rostrum not reaching to the middle coxae. 
 Wings hyaline, veins pale; stigma rather short and blunt at the apex. Stigmal vein 
 subobsolete, its course being only traced with difficulty. The distance between the 
 apex of the lower cubital branch and that of the second discoidal equal to about 
 one-half the distance between the apices of the first and second discoidals. Apterous 
 viviparous females and pupge with four rows of tubercles, each mounted with a capitate 
 bristle. 
 
 Leaves of walnut, hickory and pecan. June-July, St. Louis, Mo. 
 
 This aphis has been reported from Illinois (Thomas, 1880; Davis, 
 1910), Nebraska (Williams, 1910), Oregon (GiUette, 1910), and 
 Michigan (Gillette, 1910), and doubtless occurs in America wherever 
 its food plants grow. 
 
 GENERAL DESCRIPTION; CHARACTER AND EXTENT OF INJURY. 
 
 This aphis is about one-sixteenth of an inch long and about one- 
 third as wide and is generally of a pale lemon-yellow color. It 
 occurs on the lower surface of the leaf and on the nutlets of the 
 eastern black walnut tree and crosses derived from it. When infes- 
 tation is severe, the aphides will also be found on the upper surface 
 of the leaves. The species, according to Mr. Monell and other 
 writers, feeds also on hickories and pecan. The character and extent 
 of its injury is altogether similar to that of the European walnut 
 aphis (ChromapTiis juglandicola Kalt.). This plant-louse does not lie 
 so flatly appressed to the plant surface as the European species and 
 is much more active, bearing longer legs and antennae in proportion 
 
 1 Mr. J. T. Monell, of the Bureau of Entomology, has kindly identified the specimens sent to him by the 
 author as Monellia caryae Monell. 
 
 2 The genus Callipterus ("beautiful-winged") was erected by Koch (1855). 
 
 3 The genus Monellia was erected by Oestlund (1887), with caryella Fitch as the type species.
 
 20 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTUEE. 
 
 to the size of the body. When on. the lower surface of the leaflet it has 
 the habit of resting with the head directed straight toward the 
 peduncle of the leaflet. In July and August, in which months this 
 insect is most abundant, as many as 400 individuals may be found on 
 one leaflet, 5 per cent of which will be resting on the upper side. At 
 this time it is much sought after by ants, which feed on the liquid 
 excreted by it. A large red and black species, determined by Mr. 
 Theodore Pergande as Formica obscuriventris Mayr, is a very common 
 attendant. Formica subsericea Say also attends it. The sweet excre- 
 tions of the aphis attract many flies of the families Muscidae, Anthom- 
 yiidae, Oscinidae, and Syrphidae, many large bees including the 
 honeybee, wasps of the family Pompilidse, and parasitic wasps of the 
 families Ichneumonidse and Braconidae, and numerous smaller forms 
 of insect life. The author first observed this aphis on July 20, 1911, 
 at San Jose, Cal. 
 
 LIFE HISTORY AND TECHNICAL DESCRIPTIONS. 
 
 THE VIVIPAROUS OR ASEXUAL FORMS. 
 
 The stem-mothers hatch as soon as the buds start to swell, about 
 the 1st of April. These develop into winged aphides and pass their 
 life cycle in from 25 to 30 days, according to temperature and the 
 amount of food supply. The viviparous aphis passes through four 
 molts, becoming winged after the final one. Table VII indicates the 
 life cycle of 38 individuals of the summer generations. 
 
 TABLE VII. Life-cycle of viviparous females of Monellia caryae, summer generations, 
 San Jose, Cal, 1912. 
 
 No. of indi- 
 vidual. 
 
 Gener- 
 ation. 
 
 Date of 
 deposi- 
 tion. 
 
 Date of 
 acquiring 
 wings. 
 
 Life 
 cycle. 
 
 No. of indi- 
 vidual. 
 
 Gener- 
 ation. 
 
 Date of 
 deposi- 
 tion. 
 
 Date of 
 reaching 
 maturity. 
 
 Life 
 cycle. 
 
 1 
 2 
 
 II 
 II 
 
 Apr. 22 
 22 
 
 May 12 
 12 
 
 Days. 
 
 
 % 
 
 V 
 V 
 
 June 22 
 23 
 
 July 7 
 
 Da % 
 
 14 
 
 3 
 4 
 5 
 
 6 
 7 
 8 
 9 
 
 II 
 II 
 II 
 II 
 II 
 III 
 III 
 
 22 
 
 1 
 1 
 13 
 13 
 
 12 
 20 
 22 
 
 23 
 29 
 29 
 
 20 
 19 
 21 
 22 
 22 
 16 
 16 
 
 22 
 23 
 24 
 25 
 26 
 27 
 28 
 
 V 
 
 v 
 
 V 
 
 V 
 
 V 
 
 v 
 v 
 
 23 
 24 
 
 24 
 24 
 24 
 24 
 24 
 
 7 
 7 
 7 
 7 
 8 
 8 
 g 
 
 14 
 13 
 13 
 13 
 14 
 14 
 
 10 
 11 
 12 
 
 III 
 III 
 III 
 
 13 
 13 
 13 
 
 29 
 29 
 
 29 
 
 16 
 16 
 16 
 
 29. ... 
 30. ... 
 31. ... 
 
 V 
 
 v 
 v 
 
 25 
 25 
 25 
 
 8 
 8 
 8 
 
 13 
 13 
 13 
 
 13 
 14 
 
 15 
 
 III 
 III 
 III 
 
 13 
 13 
 13 
 
 30 
 30 
 30 
 
 17 
 17 
 17 
 
 32. ... 
 33. ... 
 34 
 
 V 
 
 v 
 v 
 
 25 
 25 
 
 27 
 
 8 
 9 
 10 
 
 13 
 14 
 13 
 
 16 
 17 
 18 
 
 19 
 
 III 
 III 
 V 
 V 
 
 13 
 13 
 June 22 
 22 
 
 30 
 30 
 July 4 
 
 17 
 17 
 12 
 15 
 
 si: ::: 
 
 36. ... 
 37. ... 
 38 
 
 V 
 V 
 
 v 
 
 VI 
 
 27 
 27 
 
 27 
 July 13 
 
 10 
 10 
 10 
 Aug 1 
 
 13 
 13 
 
 13 
 19 
 
 
 
 
 
 
 
 
 
 
 
 Thus, the second generation requires 20 days, the third 16 or 17, 
 and the fifth 15, in which to complete the life cycle. Kecords of the 
 fourth generation were not obtained owing to premature death of all
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 21 
 
 individuals of this generation of which the date of deposition had 
 been ascertained. Individuals of the fourth generation probably 
 mature in an average of 16 days. The leaves of the Eastern black 
 walnut fall earlier than those of the European or California black 
 types, and consequently the viviparous aphides are not found so late 
 on the trees. There are probably not more than nine generations of 
 these in a year. 
 
 Immediately after passing the final molt the aphides begin depos- 
 iting young. These are entirely pale lemon-yellow with red eyes 
 and four longitudinal rows of capitate hairs and do not exceed 0.70 
 mm. in length. From 10 to 20 young are produced by a single female, 
 dependent on the season of the year. The earlier generations are 
 more prolific. After midsummer the progeny becomes smaller and 
 smaller with successive broods. 
 
 THE PUPA OP THE WINGED VIVIPAROUS FEMALE (FIG. 9). 
 
 After the second molt the pupal wing pads are apparent as small 
 emarginations on the sides of 
 the thorax, but after the fol- 
 lowing molt they are much 
 more readily seen. The pupa 
 of the winged viviparous female 
 may be described as follows : 
 
 Color generally pale lemon-yellow, 
 sometimes white; head often with a 
 reddish tinge. Antennae on small 
 frontal tubercles, pale yellow, with 
 the filament and articulations of joints 
 3 to 6 dusky black. Eyes bright red. 
 Thoracic segments and wing pads 
 light yellow, wing pads projecting 
 out from the body at a very acute 
 angle. Legs pale, tarsal apices dusky. 
 Body beset with long capitate spines 
 
 in four rows. Cornicles on segment 6 
 
 .. . 
 of the abdomen, hardly perceptible, 
 
 broader than long. Cauda blunt, 
 conical, and short. Cornicles and cauda concolorous with the abdomen. Beak 
 pale, reaching to the middle coxse. Measurements: Length of body (average), 1.87 
 mm.; width of body (average), 0.71 mm.; antenna, joint I, 0.058 mm.; joint II, 0.050 
 mm.; joint III, 0.287 mm.; joint IV, 0.207 mm.; joint V, 0.201 mm.; joint VI, 0.128 
 mm.; filament, 0.136 mm. 
 
 This pupa is distinguishable from that of Chromaphis by the pres- 
 ence of the dorsal rows of spines and by the absence of the black 
 femoral spots. The penultimate instar occupies on the average four 
 or five days. At its termination the final molt occurs, and after this 
 the insect has acquired its full development. 
 
 FIG. Q.Monettia caryx: Pupa of winged viviparous 
 female (Or iginai.)
 
 22 
 
 BULLETIN 100, U. S. DEPAETMENT OF AGBICULTURE. 
 
 THE WINGED VIVIPAROUS FEMALE (FIG. 10). 
 
 General color pale lemon-yellow; many examples are greenish yellow and others 
 decidedly pinkish. Head, thoracic lobes, and scutellum pale brown or yellowish 
 brown. Eyes pink. Antennae on small frontal tubercles, about half as long as the 
 body, pale yellow, with articulations of joints III to VI black; joint III the longest, 
 not noticeably thickened basally; joint IV slightly longer than V and barely as long 
 as joint VI, together with its spur or filament. Bases of antennas encircled, in the 
 majority of individuals, with a narrow dusky ring. Close to the lateral margins of 
 the prothorax and roughly parallel to them occur two narrow black lines. (These are 
 sometimes absent.) Wings of moderate size; costa, subcosta, and stigma pale yellow- 
 ish green, other veins light brown, of medium thickness. Stigmatic vein entirely 
 subobsolete, its course not easily made out. Legs very pale, whitish, tarsi and apex 
 
 FIG. 10. Mondlia caryx: Winged viviparous female, a, Antenna. (Original.) 
 
 of tibiae dusky grey; anterior and posterior femora in about half of the individuals 
 bear a grey knee spot quite like that of Chromaphis juglandicola Kalt. but smaller. 
 This spot never occurs on the middle femora. Abdomen pale yellow, sometimes 
 greenish and at other times reddish, with four rows of small black spots, which are 
 very variable and often wholly absent. The two lateral rows have larger spots and 
 these are found on segments 2-6; the two median rows are smaller and their spots 
 exist on segments 2-8. Cornicles on segment 6, hardly perceptible, more than twice 
 as broad as long, about 0.008 mm. long. Cauda globulaV, shorter than the hind tarsus. 
 Cornicles and cauda concolorous with the abdomen. Anal plate bifid, armed with 
 spines. Beak pale, extreme tip brown and not quite extending to the second pair of 
 coxse. Sensoria occur on the antennae as follows: Joint III, 6-9 transversely oval on 
 basal half or two-thirds of joint; in an equally spaced row; joint V, 1 terminal; joint VI, 
 4 terminal (1 large, 3 small). Measurements: Length of body, 2.16 mm.; width of
 
 WALNUT APHIDES IN CALIFORNIA. 23 
 
 body, 0.754 mm.; wing expanse, 4.44 mm. Antenna, joint I, 0.076 mm.; joint II 
 0.060 mm. ; joint III, 0.416 mm. ; joint IV, 0.273 mm. ; joint V, 0.273 mm. ; joint VI, 
 0.143 mm.; filament, 0.164 mm. 
 
 Described from many specimens taken at San Jose, Cal., during 
 1911 and 1912. 
 
 The complete absence of the stigmatic vein and the relatively 
 longer antennae, together with the diminutive cornicles, will readily 
 distinguish this species from the European walnut aphid. 
 
 In 18 months' study of this plant-louse the author has failed to 
 find any trace of the existence of a wingless viviparous form. 
 
 THE OVIPAROUS OR SEXUAL FORMS. 
 
 If a tree be heavily infested, the sexual forms appear first about the 
 middle of July and probably belong to the fifth and sixth generations. 
 If infestation be only moderate or slight, these forms are not pro- 
 duced until several weeks later and will be members of the seventh 
 and following generations. The sexed forms from the beginning are 
 produced in comparative abundance and comprise from 30 to 50 
 per cent of the whole. The young sexed females are paler and more 
 spindle-shaped than the young of the viviparous individuals, while 
 the male larvss and pupae are conspicuously brick-red in color. The 
 male is not so greatly outnumbered by the female as in the European 
 walnut aphis, and from the first comprises from 20 to 30 per cent of 
 the sexed insects. On August 26 and 27 and September 5, 1912, a 
 count of the forms on 34 leaflets taken at random from an Eastern 
 black walnut tree showed 177 viviparous females, 14 males, and 26 
 sexed females. Probably as many again of the sexed females in 
 proportion to the leaflets counted could be found on the twigs 
 ovipositing. Copulation takes place on the leaf and occupies half a 
 minute. All through August and September, 1912, the oviparous 
 females were observed on the twigs, but few eggs were found until 
 September. After the middle of September few aphides were found, 
 the great majority having been destroyed by their natural enemies, 
 but those that escape perpetuate the species until the leaves fall in 
 November. The majority of aphides born in the late fall are sexual. 
 The sexed female shortly after mating becomes much swollen by 
 reason of the growing ova in her body, and the last four abdominal 
 segments become orange colored. She repairs to the twigs and limbs 
 and wanders around searching for locations wherein to oviposit. 
 Occasionally immature females wander off to the twigs, but later 
 return to the leaves to resume feeding. The fully mature fertilized 
 oviparous female once she has forsaken the leaf rarely if ever returns, 
 and thus escapes many predatory foes. Having found a crevice or 
 crack in the cortex suitable for her purpose she grips the limb with
 
 24 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGKICULTUEE. 
 
 her six legs and bends the hind part of the abdomen at a right angle 
 to the rest of the body and then gives her abdomen a succession of 
 jerks to get it into place. This performed to her satisfaction, she 
 remains motionless for 60 seconds while the egg is being extruded, and 
 after depositing it walks off. The writer has never seen the eggs of 
 this species placed in an open situation, but always in some protected 
 position in the bark. On August 28, 1912, four gravid females were 
 dissected and were found to contain respectively 3, 4, 2, and 4 large 
 eggs, and all had several smaller ones. Another had 8 large eggs in 
 her ovaries and was greatly distended therefrom. The egg is bluntly 
 oval, bright yellow when first laid, but changing in a day or two to 
 black and obscurely shining. It measures 0.35 mm. in length and 
 0.17 mm. in width, and is therefore considerably smaller than the 
 
 egg of the European walnut plant-louse. 
 
 The oviparous forms are described below. 
 
 THE OVIPAROUS FEMALE, FULL GROWN (FIG. 11 ). 
 
 General color pale greenish yellow or sometimes 
 greenish white, the four apical segments of the 
 abdomen at first colored like the rest of the body 
 and later orange colored. Body rather narrow, 
 not at all flattened, the sides nearly parallel and 
 produced posteriorly into a conical tube. An- 
 tennae a little over one-half the body in length, 
 pale, with the apical third or fourth of joints III 
 to VI dusky gray; joint II gray and armed with 
 a capitate spine on its inner margin; joint III 
 longest; joints IV and V subequal; joint VI 
 shorter than its spur or filament. Legs very pale 
 yellow, with a dark spot close to the apex of the 
 anterior and posterior femora. (In many individ- 
 uals these spots are absent.) Eyes pink. The 
 arrangement of capitate spines is as follows: The head bears eight, the prothorax 
 six, the mesothorax, metathorax, and abdominal segments 1 to 5, inclusive, 
 four, and abdominal segments 6, 7, and 8 two; these spines appear as four lon- 
 gitudinal rows. Cornicles greenish yellow, broader than long, hardly percep- 
 tible, located on segment 6. Cauda concolorous with the body, globular, armed 
 with four noncapitate spines, half as long as the hind tarsus. Genital plate protrud- 
 ing beyond the cauda, pale, its margin beset with short noncapitate hairs. Beak 
 pale, its extreme tip brownish, just exceeding the second pair of coxae. Measure- 
 ments: Length of body, 1.68 mm.; width of body, 0.72 mm.; cauda, 0.038 mm.; 
 antenna joint I, 0.04 mm.; joint II, 0.035 mm.; joint III, 0.300 mm.; joint IV, 
 0.17 mm.; joint V, 0.17 mm.; joint VI, 0.100 mm.; filament, 0.12 mm. 
 
 Described from many specimens collected at San Jose, Cal., during 
 1912. 
 
 FIG. 11. Monellia caryx: Oviparous 
 female. (Original.)
 
 WALNUT APHIDES IN CALIFORNIA. 25 
 
 YOUNG MALE PUPA. 
 
 Light red in general color; appressed closely to the leaf surface. Dorsum of head 
 in front black, behind gray. Dorsum of thorax gray. Antennae six-jointed (i. e., 
 with five joints and filament), one-third as long as the body, pale gray. Eyes bright 
 red. Legs pale, femora dusky gray. Mesothorax, metathorax, and first five abdominal 
 segments each with four black spots in a transverse row. Abdominal segments 6 to 8, 
 inclusive, with two such spots. A single capitate spine arises from each of these 
 spots. Cornicles imperceptible. Cauda pale, short, conical. Beak pale, tip dusky 
 gray, reaching first coxae. 
 
 FULL-GROWN MALE PUPA (FIG. 12). 
 
 General color t>ale brick red; head pale orange. Antennae half as long as the body, 
 seven-jointed, pale yellow, with dusky articulations. Eyes bright red. Legs very 
 pale, femora usually slightly dusky. Wing pads white. Whole body with four 
 longitudinal rows of dark capitate spines distributed as in the oviparous female. 
 Cornicles on segment 6, appearing as little rims on the body surface, broader than 
 long, concolorous with the body. Cauda bluntly conical, very short, pale yellow. 
 Beak pale yellow, extreme tip brown, reaching to the 
 first pair of coxae. Measurements: Length of body, 
 1.58mm.; width of body, 0.57mm.; cauda, 0.045mm. 
 Antenna, joint I, 0.071 mm.; joint II, 0.054 mm.; 
 joint III, 0.257 mm.; joint IV, 0.173 mm.; joint Y, 
 0.200 mm. ; joint VI, 0.12 mm. ; filament, 0.12 mm. 
 
 Described from several specimens col- 
 lected at San Jose, Gal., in 1912. 
 
 WINGED MALE (FIGS. 13; 18, a). 
 
 General color pale lemon-yellow or greenish yellow ; 
 head and a median quadrilateral area on thorax dark 
 brown; scutellum dark brown; eyes dark red. An- 
 tennae not mounted on frontal tubercles, about as long 
 
 asthebody; jomts I and II with a dusky central part; ^ 12 __ 3Mfl Malepupa> 
 
 joints III to VI pale, with their apices dusky gray; (Original ) 
 
 filament pale; joint III longest, bearing about 24 
 
 small oval sensoria; joints IV and V subequal, both bearing 10 to 15 small sensoria 
 arranged along the outer margin; joint VI bearing 4 sensoria, of which the most 
 distal is apical; joint VI longer than the filament, the two together scarcely as 
 long as joint V. Ocelli distinct. Wings of medium size; costa and insertions 
 greenish yellow; stigma short and moderately broad, dusky gray, with a large paler 
 central area; veins brown, the third discoidal curving considerably to meet its 
 second fork; second fork twice as near to the first fork as to the apex of the wing; 
 stigmatic vein obsolete in its middle portion. Legs longer in proportion to the body 
 than in the winged viviparous female, pale greenish yellow, with a large dusky area 
 near the apex of all six femora; apices of tibiae and tarsi dusky gray. Abdomen 
 short,' not quite as long as the head and thorax together, widest at the third segment; 
 segments 1 to 7, inclusive, with two lateral black spots, one on each side; segments 
 1 to 6, inclusive, and segment 8 with two dorsal black spots, one on either side of the 
 dorso-median line; the lateral spots on segments 1 to 6, inclusive, are circular or sub- 
 circular; the dorsal pairs on these segments are oval; the dorsal spots on segments 6 
 and 8 coalesce narrowly in the middle. Cornicles on segment 6, hardly perceptible, 
 broader than long. Cauda globular, dusky, half as long as the hind tarsus. Repro-
 
 26 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 ductive organ white, when extended about as long as antennal joint IV. Beak pale 
 yellow, extending a little beyond the first pair of coxae. Sterna and apical half of 
 the underside of the head dark brown. Very often one or more of the dusky abdominal 
 spots are absent. Measurements: Length of body, 1.39mm.; width of body, 0.69mm.; 
 wing expanse, 4.10 mm.; cauda, 0.049 mm.; antennal joint I, 0.051 mm.; joint II, 
 0.058 mm.; joint III, 0.362 mm.; joint IV, 0.238 mm.; joint V, 0.240 mm.; joint 
 VI, 0.114 mm.; filament, 0.134 mm. 
 
 Described from four specimens collected at San Jose, Cal., in 1912. 
 
 FIG. 13. AfonfM/a carya;.- Winged male, a, I^eft antenna. (Original.) 
 
 THE LITTLE HICKORY APHIS (Monellia caryella Fitch). 
 
 Aphis caryella Fitch, [First] Report on the noxious, beneficial, and other insects 
 
 of the State of New York, Albany, p. 163-165, 1855. 
 Callipterus caryellus Fitch, Third report on the noxious and other insects of the 
 
 State of New York, Albany, p. 448-449, 1856. 
 Monellia caryella, Oestlund, Geol. & Nat. Hist. Survey Minn. Bui. 4, p. 45, 1887. 
 
 HISTORY OF THE SPECIES. 
 
 The little hickory aphis was first collected in New York State by 
 Dr. Asa Fitch, previous to the year 1855. The following is Fitch's 
 original description: 
 
 The Little Hickory Aphis (Aphis caryella) is pale yellow with white antennae which 
 are alternated with black rings, the wings are transparent and without spots, their 
 veins slender and pale yellow, the legs yellowish white to their ends. Length 0.12 
 to the tips of the wings. The abdomen is depressed, egg-shaped, its apex slightly
 
 WALNUT APHIDES IN CALIFORNIA. 27 
 
 narrowed and elongated. The antennae are longer than the body, tapering, seven- 
 jointed; two basal joints as broad as long, twice the diameter of the following joints; 
 third joint longest, slightly thicker towards its base; fourth and fifth joints rather shorter 
 than the third, cylindric; two last joints together about equalling the fifth in length; 
 the sixth swelled at its tip into a long oval knob, the seventh more slender but not 
 capillary, shorter than the sixth ; a broad black band at the base of the third and each 
 of the following joints. First vein of the fore wings straight and almost transverse; 
 second vein bent near its base, running first towards the apex and then turning rather 
 abruptly and continuing straight to the inner margin, more than twice as far from the 
 first at tip as base; third vein arising from the stigma near its anterior end, and not 
 from the rib- vein forward of the stigma, as it does in the aphides generally, except 
 those pertaining to this group, its base and its apex about the same distance from the 
 second vein that this is from the first, forking rather forward of its middle, strongly 
 bent at this point, and from hence to its i ip parallel with the third vein or but slightly 
 diverging from it, its tip a third nearer that of the third vein than this is to the second; 
 second fork nearer the fourth vein at tip than to the first fork, the triangular cell be- 
 tween it and the first fork with its three sides equal; fourth vein short and often nearly 
 abortive, shorter than the second fork, equally curved through its whole length, its 
 tip much nearer that of the rib-vein than that of the second fork; rib- vein very slightly 
 diverging from the margin from the base to the stigma, curved from thence to its tip. 
 Stigma oval, about twice as long as wide, watery, sometimes tinged with yellowish. A 
 variety has the stigma dusky at its tip. Another variety (costalis) has the rib-vein 
 coal black interrupted with whitish towards the stigma, which is dusky and black at 
 each end. 
 
 In a general discussion of this species before his description Fitch 
 refers to the minute cornicles characteristic of this and kindred 
 species. In his third report on the insects of New York he mentions 
 the European walnut aphis and says "European C. juglandicola of 
 Koch" [ChromapMs juglandicola Kalt.] " appears closely related to 
 this present species" [i. e. Callipterus caryellus]. Fitch gave the 
 host plant of his species as the hickory. Oestlund (1887) reports it 
 ^Minnesota from Carya amara'Nutt. Davis (1910) and other Eastern 
 writers record it from hickory in the Eastern States. In California 
 the normal food plants are the California black walnut (Juglans 
 calif ornica) and hybrids derived from this tree. 
 
 GENERAL APPEARANCE; CHARACTER AND EXTENT OF INJURY. 
 
 In general appearance this aphis is very similar to the American 
 walnut aphis (Monellia caryse Monell) and can not be distinguished 
 from it except when viewed under the microscope or a powerful hand 
 magnifier. Its habits of life and the character and extent of its 
 injury are also very similar to those of M. caryse. The writer had 
 observed this aphis for several months before he realized that it was a 
 distinct species and not a variety of caryse, as he had previously 
 supposed. When the sexed forms appeared it was noticed that the 
 oviparous female of caryella differed markedly from the same form 
 of caryse, and this led to a closer scrutiny of the viviparous form 
 resulting in the establishment of the points of divergence shown in 
 Table VIII.
 
 28 
 
 BULLETIN 100, TJ. S. DEPARTMENT OF AGEICULTUEE. 
 
 TABLE VIII. Divergences of structure between Monellia caryse Monell and M. caryella 
 
 Fitch. 
 
 Form. 
 
 Monellia caryx Monell. 
 
 Monellia caryella Fitch. 
 
 Winged viviparous female 
 
 Pupa of viviparous female 
 Oviparous female 
 
 Antennal joint III very slightly 
 thickened basally. 
 Sensoria on antennal joint III 
 occupying basal half or two- 
 thirds. 
 Antennal joint VI and its spur or 
 filament subequal, or VI less 
 than spur. 
 Dusky knee spots often present. 
 Four longitudinal rows of capitate 
 spines. 
 Smaller than the viviparous fe- 
 
 Antennal joint III quite notice- 
 ably thickened for its basal half. 
 Sensoria on antennal joint III oc- 
 cupying basal third. 
 Antennal joint VI one-third as 
 long again as its spur or filament. 
 Dusky knee spots absent. 
 
 Six longitudinal rows of capitate 
 spines. 
 Larger than the viviparous fe- 
 
 
 male. 
 Four longitudinal rows of capitate 
 spines. 
 
 male. 
 Six longitudinal rows of capitate 
 spines. 
 
 LIFE HISTORY AND TECHNICAL DESCRIPTIONS. 
 
 Life-history studies on this plant-louse began in August, 1912, at 
 San Jose, Cal., but no rearing work was done until the appearance 
 of the sexed forms in September. Observations taken in August 
 and September indicated a development of the summer generations 
 similar to that found in Monellia caryse. This was further confirmed 
 by studies during 1913. The sexed forms were studied at Walnut 
 Creek and San Jose, Cal. In both localities these did not appear until 
 late in September, even on trees heavily infested. The aphides re- 
 mained on the trees as long as there were leaves on which they could 
 subsist and were to be found until mid-November. After September 
 the great majority of aphides deposited were oviparous, and of these 
 the males were extraordinarily scarce, the writer observing only one 
 individual of this sex among hundreds of oviparous females. Table 
 IX indicates the life cycle of plant-lice deposited by four viviparous 
 females and shows the preponderance of the sexed form over the 
 asexual in the late fall. 
 
 TABLE IX. Life-cycle record of the progeny of four viviparous females of Monellia 
 
 caryella, Walnut Creek, Cal., 1912. 
 FEMALE NO. 1; DEPOSITED 3 YOUNG. 
 
 
 
 
 Date of 
 
 
 
 
 
 No. of larva. 
 
 Hatch- 
 ing. 
 
 Molt 1. 
 
 Molt 2. 
 
 Molt 3. 
 
 Molt 4 
 (beconi- 
 
 adult). 
 
 Form of individual. 
 
 Life 
 cycle. 
 
 l 
 
 Oct. 4 
 
 Oct. 7 
 
 Oct. 10 
 
 (?) 
 
 Oct. If. 
 
 Winged viviparous fe- 
 
 *% 
 
 
 
 
 
 
 
 male. 
 
 
 2 
 
 4 
 
 7 
 
 11 
 
 (?) 
 
 18 
 
 Oviparous female 
 
 14 
 
 31 
 
 
 
 
 
 
 .do .. 
 
 
 
 
 
 
 
 
 
 
 FEMALE NO. 2; DEPOSITED 6 YOUNG. 
 
 1 
 
 Oct 12 
 
 Oct 15 
 
 Oct 18 
 
 Oct. 21 
 
 Oct. 28 
 
 Oviparous female 
 
 16 
 
 2 
 
 12 
 
 15 
 
 18 
 
 21 
 
 28 
 
 do 
 
 16 
 
 
 12 
 
 15 
 
 19 
 
 22 
 23 
 
 29 
 30 
 
 ....do 
 
 do 
 
 17 
 18 
 
 5 
 
 12 
 
 (?) 
 
 (?) 
 
 (?) 
 
 29 
 
 ....do... 
 
 17 
 
 6 
 
 12 
 
 (?) 
 
 (?) 
 
 (?) 
 
 30 
 
 .do 
 
 18 
 
 
 
 
 
 
 
 
 
 i Died permaturely.
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 29 
 
 TABLE IX. Life-cycle record of th> 
 caryella, Walnut 
 
 ny of four viviparous females of Monellia 
 * ' , 1912 Continued. 
 
 FEMALE NO. 3; DEPOSITED 16 YOUNG. 
 
 
 
 
 Date of 
 
 
 
 
 
 No. of larva. 
 
 Hatch- 
 ing. 
 
 Molt 1. 
 
 Molt 2. 
 
 Molt 3. 
 
 Molt 4 
 (becom- 
 ing 
 adult). 
 
 Form of individual. 
 
 Life 
 cycle. 
 
 
 Oct 16 
 
 Oct 21' 
 
 Oct 27 
 
 Nov 3 
 
 
 
 Days. 
 
 2 
 
 16 
 
 21 
 
 27 
 
 3 
 
 7 
 
 do 
 
 22 
 
 3 
 
 16 
 
 21 
 
 27 
 
 3 
 
 7 
 
 do 
 
 22 
 
 4 
 
 17 
 
 (?) 
 
 (?) 
 
 (?) 
 
 g 
 
 do 
 
 22 
 
 5 
 
 17 
 
 ? 
 
 ?) 
 
 ? 
 
 
 do 
 
 22 
 
 6 
 
 17 
 
 \1 
 
 ?) 
 
 (?) 
 
 g 
 
 do 
 
 22 
 
 7 
 
 17 
 
 ? 
 
 ? 
 
 (?) 
 
 g 
 
 do 
 
 22 
 
 8 
 
 18 
 
 ? 
 
 rj 
 
 ? 
 
 g 
 
 do 
 
 21 
 
 9 
 10 1 
 
 18 
 
 ? 
 
 ? 
 
 (?) 
 
 9 
 
 do 
 
 ... .do 
 
 22 
 
 Hi 
 
 
 
 
 
 
 do 
 
 
 12 > 
 
 
 
 
 
 
 do 
 
 
 13 1 
 
 
 
 
 
 
 do 
 
 
 141 
 
 
 
 
 
 
 do 
 
 
 15 i 
 
 
 
 
 
 
 do 
 
 
 161 
 
 
 
 
 
 
 do. 
 
 
 
 
 
 
 
 
 
 
 FEMALE NO. 4; DEPOSITED g YOUNG. 
 
 1 
 
 Oct 18 
 
 Oct 22 
 
 Oct 27 
 
 Nov 2 
 
 Nov 
 
 Ovi arous female 
 
 
 2... 
 
 lg 
 
 22 
 
 27 
 
 3 
 
 9 
 
 do 
 
 22 
 
 3 
 
 18 
 
 22 
 
 27 
 
 
 g 
 
 do 
 
 22 
 
 4 
 
 18 
 
 22 
 
 27 
 
 4 
 
 9 
 
 do 
 
 22 
 
 51 
 
 
 
 
 
 
 do 
 
 
 9. 
 
 
 
 
 
 
 do 
 
 
 71 
 
 
 
 
 
 
 do 
 
 
 gi 
 
 
 
 
 
 
 do 
 
 
 
 
 
 
 
 
 
 
 Died prematurely. 
 SUMMARY. 
 
 Life cycle (20 oviparous females). 
 
 Days. 
 
 
 22 
 
 Minimum 
 Average ... 
 
 14 
 18 92 
 
 First instar (13 individuals), average. . . 
 Second instar (13 individuals), average.. 
 Third instar (11 individuals), average... 
 Fourth instar (11 individuals), average . 
 
 3.7 
 4.5 
 5.7 
 5.6 
 
 The viviparous forms, so far as the author has observed, all 
 develop wings. 
 
 The eggs of this aphis are larger than those of the American walnut 
 aphis and measure on the average 0.536 mm. in length and 0.222 mm. 
 in maximum width. They are elongate-oval in shape, rather feebly 
 shining, and have a softer shell than is found in the eggs of the 
 majority of plant-lice, but one not so soft as is that of (Jhromaphis 
 juglandicola. They are placed either singly or in groups of two or 
 three around the axils of the buds or in crevices in the bark and in 
 scars caused by fallen leaves on the smaller limbs and twigs. Ovipo- 
 sition is in. progress during the months of October and November, each 
 oviparous female laying on the average about 12 eggs. Owing to the
 
 30 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 scarcity of males in the fall of 1912 at Walnut Creek, Cal., it seemed 
 very probable that a large proportion of the eggs would prove to be 
 sterile, and in the following spring examinations of egg-infested trees 
 showed this assumption to be correct. 
 
 THE VIVIPAROUS FORMS. 
 
 The stem-mothers commence hatching very shortly after the leaf 
 buds open in the latter part of March. Previous to the first molt 
 they are pale lemon-yellow with red eyes, hyaline legs, and dusky 
 tarsi; the joints of the antennae have black articulations; on the 
 abdomen are four longitudinal rows of circular dusky spots from each 
 of which arises a capitate spine. They are destined to become winged 
 and in their later stages do not differ from the summer winged 
 viviparous individuals. 
 
 FIG. 14. Monellia caryella: Tupa of winged viviparous female. (Original.) 
 THE PUPA OP THE WINGED VIVIPAROUS FEMALE (FIG. 14). 
 
 General color pale lemon-yellow; some individuals exhibit a decided greenish, 
 others a decided salmon colored tinge. Antennae two-thirds of the body in length; 
 apices of joints III to VI and the whole filament dusky, otherwise pale yellow, almost 
 white. Eyes bright red. Head with eight capitate spines, six of these on the frontal 
 margin and two near the hind border. Prothorax with six capitate spines, two of 
 these near the middle of the segment and four in a transverse row along the hind 
 margin. Mesothorax, metathorax, and abdomen with six longitudinal rows of capitate 
 spines. Legs pale yellow, tarsi dusky. Wing pads pale, after being imbedded in 
 balsam for a few days becoming dusky. Cornicles barely perceptible, wider than 
 long. Cauda rounded, not as long as the hind tarsi and without hairs. Beak pale 
 with a brown tip, almost reaching the second pair of coxae. Measurements: Length 
 of body, 1.81 mm.; width of body, 0.72 mm.; antenna, joint I, 0.070 mm.; joint n, 
 0.050 mm.; joint III, 0.253 mm.; joint IV, 0.198 mm.; joint V, 0.183 mm.; joint VI, 
 0.134 mm.; filament, 0.105 mm. 
 
 Described from four specimens, Walnut Creek, Cal., October, 1912.
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 31 
 
 THE WINGED VIVIPAROUS FEMALE (FIG. 15). 
 
 General color pale lemon-yellow, somewhat varying in shade. Antennae about 
 four-fifths as long as the body, pale yellow, with joints III to VI, inclusive, bearing 
 an apical black ring (on joint III this ring is narrower than the other joints); fila- 
 ment of joint VI dusky; joint III is the longest; joints IV and V subequal or joint IV 
 slightly longer than V; joint IV about four-fifths as long as III; joint VI together with 
 its filament about equal to V; filament about three-fourths as long as VI; basal third 
 of joint III noticeably swollen and bearing from five to seven oval transverse eensoria; 
 usual apical sensoria on both joints V and VI. Head pale yellow, with the frontal 
 margin black. Eyes bright red. Prothorax pale yellow, with two narrow, black, 
 longitudinal stripes arising from the anterior angles and extending for two-thirds 
 
 FIG. 15. Monellia caryetta: Winged viviparous female, a, Right antenna, enlarged, with variations of 
 number of sensoria. (Original.) 
 
 of its width. Thoracic lobes and scutellum light brown, sometimes with a salmon- 
 pink tinge. Wing insertions, costa, subcosta, and stigma pale lemon-yellow; dis- 
 coidals yellowish -brown; first and second discoidals heavier than the other veins; 
 third discoidal obsolete at its immediate base, its first fork equidistant from the 
 second fork and the base of the discoidal, its second fork nearer to the first fork than 
 to the apices of its two branches; branches of second fork equal in length; stigmatic 
 vein very weak, its basal half traceable only with difficulty; lower wing colorless. 
 Legs pale yellow; tarsi and tibial apices dusky. Abdomen entirely pale lemon- 
 yellow, the body widest at the third segment. Body somewhat narrowed laterally. 
 Cornicles pale yellow, hardly perceptible, wider than long. Cauda globular, bearing 
 a fringe of weak hairs, about equal in length to the hind tarsi, concolorous with the 
 abdomen. Genital plates armed with weak hairs, pale yellow. Beak pale yellow, 
 its extreme tip brown, extending halfway between first and second coxae. Measure-
 
 32 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 mente: Length of body (average), 1.67 mm.; width of body (average), 0.61 mm.; 
 wing expanse (average), 4.02 mm.; antenna, joint I, 0.053 mm.; joint II, 0.046 mm,; 
 joint III, 0.41 mm.; joint IV, 0.335 mm.; joint V, 0.32 mm.; joint VI, 0.191 mm.; 
 filament, 0.123 mm.; cauda, 0.084 mm.; Cornicles, 0.009 mm. 
 
 Described from numerous specimens, Walnut Creek, Cal., October, 
 1912. 
 
 THE OVIPAROUS FORMS. 
 
 THE OVIPAROUS FEMALE (FIG. 1C). 
 
 Wingless. General color pale lemon-yellow, in mature individuals the central part 
 of the abdomen diffused with orange. Body elliptical, "widest at the third abdominal 
 jnt. Antennae half as long as the body, not on frontal tubercles, pale, with 
 
 FiQ. 16. Monellia carydla: Oviparous female. (Original.) 
 
 an apical black ring on joints III to VI, inclusive; joints I,' II, and filament dusky; 
 joint III longest; joints IV and V subequal and each about four-fifths as long as joint 
 III ; filament a little shorter than VI ; VI about four-fifths as long as V. Eyes crimson. 
 Legs pale yellow; tarsi dusky. Hind tibiae slightly thickened. Cornicles very 
 small, pale. Cauda pale, globular, beset with a fringe of weak hairs, not as long as 
 the hind tarsi. Thorax and abdomen with six longitudinal rows of capitate bristles, 
 each surmounting a pale tubercle. Penultimate segment of the abdomen encircled 
 near its posterior margin with a fringe of weak hairs. Eight capitate spines on the
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 33 
 
 head and six on the prothorax. Tibia? armed with a row of short bristles on their 
 inner margins. Beak pale, the extreme tip dusky, extending a little beyond the 
 anterior coxae. The young oviparous female is entirely pale yellow and can be dis- 
 tinguished from the young viviparous female only by its more eliptical shape, that 
 of the latter being more oval. Measurements: Length of body, 1.89 mm.; width of 
 body, 0.92 mm. ; antenna, joint I, 0.075 mm. ; joint II, 0.042 mm. ; joint III, 0.312 mm. 
 joint IV, 0.203 mm.; joint V, 0.218 mm.; joint VI, 0.167 mm.; filament, 0.108 mm. 
 cauda, 0.080 mm.; cornicles, 0.009 mm. 
 
 Described from numerous specimens, Walnut Creek, Cal., October, 
 1912. 
 
 WINGED MALE (FIGS. 17; 18, 6). 
 
 General color pale green or greenish yellow. Head and prothorax olive-green. 
 Frontal margin of head and frontal margin of prothorax, black. Prothorax with two 
 
 FIG. l7. Monelliacaryella: Winged male. (Original.) 
 
 bluntly rounded dusky tubercles on the dorsum. Dorsum of head and thorax with 
 indefinite dusky markings. Eyes red. Antennae dark olive-green, about three- 
 fourths of the body in length; joint VI longer than its filament. Sensoria as follows: 
 III,about21:IV,7to9;V,6tolO;VI,2to4(besidestheusualapical). Wings of mod- 
 erate size; insertions and subcosta greenish-yellow; stigma light brown, with a paler 
 central area ; discoidals 1 and 2 thicker than the other veins and with a narrow smoky 
 border; stigma tic vein obsolete except for its apical third; veins brown. Legs pale 
 greenish-yellow; coxae, trochanters, apical five-sixths of femora, and basal four-fifths 
 of tibiae black; tarsi gray. Thoracic lobes and scutellum black. Under the wings
 
 34 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 f- ; 
 
 FIG. 18. a, Monettia cargo:, antenna of male; 
 6, Monettia caryella, two views of right an- 
 tenna of male. (Original.) 
 
 occurs a large black spot on the pleurae. 
 Abdomen unarmed, pale green or green- 
 ish yellow; segments 1 to 8, inclusive, 
 with two dusky brown oval spots on 
 each. Cornicles pale, concolorous with 
 the body, very small, considerably 
 broader than long. Cauda concolorous 
 with the abdomen, globular. Abdomen 
 about as long as head and thorax com- 
 bined, not wider than the thorax. 
 Beak pale, barely reaching second 
 coxse. Sternum and underside of the 
 eighth abdominal segment black.' 
 
 Measurements: Length of body, 1.57 
 mm.; width of body, 0.62 mm.; ex- 
 panse of wings, 4.62 mm.; antenna, 
 joint I, 0.080mm.; joint II, 0.041 mm.; 
 joint III, 0.412 mm.; joint IV, 0.317 
 mm.; joint V, 0.260 mm.; joint VI, 
 0.175 mm.; filament, 0.108mm.; cauda, 
 0.067 mm.; cornicles, 0.009 mm. 
 
 Described from three speci- 
 mens, Walnut Creek, Cal., 1912 
 and 1913. 
 
 MONELLIA CALIFORNICA Essig. 
 
 Monellia californiais Essig, Pomona 
 Jour. Ent.,v.4, no. 3, p. 767, Nov., 
 1912. 
 
 In southern California feeding 
 on the underside of the leaves of 
 the California black walnut 
 (Juglans californica) there has 
 recently been found a plant- 
 louse closely allied to MoneUia 
 caryse and M. caryella. The 
 writer has never seen this aphis 
 in nature, but has received speci- 
 mens from Mr. Essig, who de- 
 scribed it. 
 
 KEY TO THE SPECIES OF MONEL- 
 LIA KNOWN TO OCCUR IN CALI- 
 FORNIA. 
 
 The following key will serve 
 to distinguish the four species 
 of walnut aphides occurring in 
 California.
 
 WALNUT APHIDES IN CALIFORNIA. 35 
 
 KEY TO THE SPECIES OF APHIDID^E KNOWN TO OCCUR ON WALNUT IN CALIFORNIA. 
 
 A. Cornicles quite evident, about as wide as long. 
 
 Chromaphis juglandicola Kalt. 
 
 AA. Cornicles barely perceptible, considerably wider than long. 
 B. Tibiae of winged viviparous female entirely dusky. 
 
 Monellia californica Essig. 
 BB. Tibiae of winged viviparous female for the most part pale. 
 
 C. Filament of joint VI longer than joint VI ; oviparous female with 
 
 four longitudinal rows of capitate hairs Monellia can/at Monell. 
 
 CC. Filament of joint VI shorter than joint VI; oviparous female with 
 six longitudinal rows of capitate hairs Monellia caryella Fitch. 
 
 NATURAL CONTROL OF WALNUT APHIDES. 
 
 INTERNAL PARASITES. 
 
 In July, 1912, a small chalcidid wasp was observed ovipositing in 
 a pupa of Monellia caryse. This is the only record of parasitism or 
 attempted parasitism observed during two seasons, so there is good 
 reason to believe that these aphides are practically immune from the 
 attacks of internal parasites. 
 
 FUNGOUS DISEASES. 
 
 Although occasionally a plant-louse may be noticed here and there 
 killed by fungus, only a single instance of the destruction of a colony 
 by this agency came under the writer's notice. This occurred on 
 May 20, 1911, following a rainstorm, and all the plant-lice on a few 
 leaves were destroyed. The disease did not spread far, some cause 
 or other checking the fungus shortly after its appearance. 
 
 PREDACEOUS ENEMIES. 
 
 Predaceous enemies are of prime importance in the control of 
 plant-lice on walnuts and where the aphides occur hi any numbers 
 may always be found preying on them from June to September. 
 Unfortunately they do not make their appearance on the walnuts 
 until their prey has had tune to do much damage to young nuts and 
 to become abundant enough to cause collective injury to the tree. 
 Should these predaceous forms appear in early spring they would 
 quickly wipe out the few plant-lice present at that time and conse- 
 quently their progeny would starve to death. As injury is thus done 
 to the nuts and to the vitality of the tree before the advent of natural 
 enemies, artificial measures must be practiced in order to insure 
 healthy trees and perfect nut crops. 
 
 The predaceous enemies of walnut plant-lice include syrphus-fly 
 larvae, agromyzid larvae, chrysopid and hemerobid larvae, coccinellid 
 beetles and their larvae, Camptobrochis brevis Uhler (Heteroptera) and 
 its larva, and various spiders.
 
 36 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 SPIDERS. 
 
 The commonest spider predaceous on walnut plant lice is The- 
 ridium placens Keyserling. This spider may be found on the trees 
 during the months of August and September and has a habit 
 of curling around itself the edge of the leaf under the protec- 
 tion of which to deposit its egg sac. This species was determined 
 by Mr. Nathan Banks, of the Bureau of Entomology, who says of it 
 "* * * a species found on the Pacific coast. They do not 
 choose their food, but from location of web are apt to get many 
 plant lice." This and other spiders are of comparatively small 
 economic importance in the control of aphides. 
 
 CAMPTOBROCHIS BKEVIS UHLER. 
 
 Camptobrochis brevis Uhler, which was determined by Mr. Otto 
 Heidemann, of the Bureau of Entomology, is a small black capsid, 
 measuring in the adult stage 4.2 by 1.9 mm. Its larva is white, with 
 conspicuous black markings. Both immature and mature individ- 
 uals were observed actively and abundantly attacking plant lice 
 during August, 1912. They do not occur in numbers earlier in the 
 year and disappear in September. Thus their beneficial work is 
 
 limited. 
 
 LEUCOPIS sp. 
 
 A fly of the family Agromyzidse, Leucopis sp., in ite larval state 
 preys upon walnut plant lice from June to August. The small 
 yellow maggots superficially resemble syrphid larvae. They are 
 never very abundant and are not a great factor in the control of the 
 "lice." The life cycle in summer is completed in 24 days or less 
 and there are several broods in California. 
 
 CHRYSOPID OR LACEWING FLIES. 
 
 Of scarcely less importance economically than the ladybird beetles 
 and syrphid maggots are the active reddish-brown larvae of the " lace- 
 wings." CJirysopa majescula Banks and C. californica Coq. are two 
 species of economic importance in California. Table X shows the 
 predatory activities of two larvae of the latter species in the fall of 
 1912. The aphides consumed by these larvae were of all sizes and 
 averaged about 1.5 by 0.5 mm. 
 
 TABLE X. Chrysopa californica: Predatory activities on walnut plant lice, Walnut 
 Creek, Cal., 1912. 
 
 
 Date of 
 
 
 
 
 
 Number 
 
 
 
 Larva 
 No. 
 
 
 Number 
 "lice" 
 eaten to 
 molt 1. 
 
 Date of 
 molt 2. 
 
 Number 
 "lice" 
 eaten, 
 molt 1 to 
 molt 2. 
 
 Date of 
 spinning 
 cocoon. 
 
 "lice" 
 eaten 
 from 
 molt 2 
 
 to issr 
 
 Total 
 "lice" 
 eaten. 
 
 Num- 
 ber 
 days 
 feed- 
 ing. 
 
 Hatch- 
 ing. 
 
 Moltl. 
 
 1 
 
 Sept. 18 
 
 Sept. 22 
 
 11 
 
 Sept. 27 
 
 70 
 
 Oct. 8 
 
 265 
 
 346 
 
 20 
 
 2 
 
 18 
 
 21 
 
 22 
 
 26 
 
 57 
 
 7 
 
 300 
 
 379 
 
 19
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 37 
 
 Larva No. 1 ate on the average 17.3 "lice" per day, while larva 
 No. 2 consumed 19.9 "lice" per day. The lacewing larvae appear 
 in numbers toward the end of June and may be found until the end 
 of October. There are probably at least three broods, the last one 
 wintering in the cocoon, which is white, short oval, with a central 
 brown annulation, and is spun among the leaves or under a piece of 
 bark. The closely allied but smaller hemerobiid larvae also attack 
 
 walnut plant lice. 
 
 SYRPHID LARVAE. 
 
 Next to the ladybird beetles the larvae of flies of the family 
 Syrphidae are of greatest importance in the natural control of walnut 
 aphides. The author has reared the following species of Syrphidae 
 from larvae collected while they were feeding on walnut aphides: 
 Catabomba pyrastri Linnaeus (1911-12) ; Sph&rophoria, melanosa Wil- 
 liston (Aug. 24, 1912); SpJiseropJioria sulpJiuripes Thomson (Oct. 15, 
 1911); Allograpta obliqua S&y (Aug. 6, 1912); Eupeodes volucris Osten 
 Sac ken (July, 1911). SyrpJius opinator Osten Sacken, and probably 
 other members of this genus, prey on the aphides. Catabomba pyrastri 
 is the most abundant as well as the largest of these flies. Its aphido- 
 phagous capacity is almost double that of any of the other species 
 enumerated above. Table XI indicates the predatory activities of 
 two larvae of the last brood of this fly. 
 
 TABLE XI. Catabomba pyrastri: Predatory activities on walnut plant lice, Santa Jose, 
 
 Cal., 1912. 
 
 Date. 
 
 Number of 
 "lice" eaten 
 by- 
 
 Date. 
 
 Number of 
 "lice" eaten 
 by- 
 
 Date. 
 
 Number of 
 "lice "eaten 
 by- 
 
 Larva 
 No. 1. 
 
 Larva 
 
 No. 2. 
 
 Larva 
 No. 1. 
 
 Larva 
 No. 2. 
 
 Larva 
 No. 1. 
 
 Larva 
 No. 2. 
 
 Aue 29 
 
 0) 
 4 
 
 (') 
 
 4 
 
 Sept.9 
 10 
 
 53 
 65 
 76 
 17 
 70 
 62 
 84 
 74 
 71 
 
 59 
 85 
 62 
 20 
 83 
 77 
 63 
 83 
 105 
 
 Sept. 18 
 
 92 
 50 
 36 
 35 
 
 2 14 
 
 107 
 104 
 10 
 
 213 
 
 30"" 
 
 P 19 
 
 31 
 
 15 
 20 
 12 
 11 
 11 
 23 
 68 
 
 15 
 15 
 17 
 17 
 18 
 36 
 46 
 
 11 
 
 20 
 21 
 22 
 
 Sept. 2 
 
 4 
 
 12 
 13 
 14 
 
 Total 
 
 
 
 5 
 6 
 
 15 
 16 
 17 
 
 959 
 
 1,035 
 
 
 Hatched on this date. 
 
 1 Pupated on this date. 
 
 The "lice" consumed were of a similar average size to those eaten 
 by the chrysopid larvae (Table X). The larva of Catabomba pyrastri 
 is pale green, with three longitudinal white stripes the whole length of 
 the body, and when fully extended exceeds half an inch in length. 
 The anterior segments of the body are retractile, giving it a sluglike 
 appearance. If food is plentiful the larva moves but little, although it 
 is capable of rapid crawling over the foliage if food is scarce. A para- 
 site, Bassus sp., preys upon it, often destroying as much as two-thirds 
 
 243747
 
 38 
 
 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 of a brood and thus reducing its economic value. The maggot of the 
 fly pupates commonly among fallen leaves or rubbish at the base of 
 the tree, forming a light brown puparium (sometimes dark purplish- 
 brown, in which case the specimen is parasitized), with a paler 
 median longitudinal stripe. The adult fly is a large, shining black 
 form, with three interrupted, pale-yellow, arcuate cross-bands 
 (rarely wanting), and is 12 mm. long. Syrphid larvae may be found 
 preying upon walnut plant lice from May to November, although 
 they are quite scarce in the two extreme months. 
 
 LADYBIRD BEETLES (FAMILY COCCINELLHXS:). 
 
 Ladybird beetles are the principal enemies of aphides affecting 
 walnuts. The author has observed the following species feeding on 
 these aphides: (1) Olla dbdominalis Say; (2) Adalia melanopleura 
 Le Conte; (3) Cocdnella Juliana Mulsant; (4) Adalia Jiumeralis Say; 
 (5) Hippodamia convergent Guerin; (6) Hippodamia ambigua Le 
 Conte; (7) Cocdnella calif ornica Mannerheim; (8) Adalia bipunctata 
 Linnaeus; (9) CJiilocoms orbus Casey. Nos. 1 to 8 in both adult 
 and larval stages feed on the plant lice on the leaves, while the adults 
 of the Chilocorus occasionally attack the winter eggs on the limbs. 
 Nos. 1 to 4 are the most persistent enemies of the aphides, the others 
 only appearing spasmodically on the trees. The Hippodamia group 
 of lady birds seems to prefer such intensely gregarious plant lice as 
 the plum louse (Hyalopterus arundinis Fabricius) or the bean aphis 
 (Aphis rumitis Linnaeus) and pay much less attention to the more 
 sporadic varieties such as the aphides on walnuts. 
 
 Table XII indicates the predatory activities of five larvae of Olla 
 abdominalis (the ashy-gray ladybird.) 
 
 TABLE XII. Olla abdominalis: Predatory activities on walnut plant lice, San Jose, 
 
 Cal, 1912. 
 
 
 
 
 Num- 
 
 
 Num- 
 
 
 Num- 
 
 
 
 
 Larva 
 No. 
 
 Date of 
 hatching. 
 
 Date of 
 molt 1 . 
 
 ber of 
 "lice" 
 eaten 
 to molt 
 
 Date of 
 molt 2. 
 
 ber of 
 "lice" 
 eaten, 
 molts 1 
 
 Date of 
 molt 3. 
 
 ber of 
 "lice" 
 eaten, 
 molts 
 
 Date of 
 pupation . 
 
 Total 
 "lice" 
 eaten. 
 
 Date of 
 adult 
 emer- 
 
 
 
 
 1. 
 
 
 and 2. 
 
 
 2 to 3. 
 
 
 
 
 1 
 2 
 
 Aug. 27 
 
 Aug. 30 
 Sept. 5 
 
 29 
 38 
 
 Sept. 2 
 9 
 
 36 
 30 
 
 Sept. 5 
 12 
 
 91 
 45 
 
 Sept. 13 
 19 
 
 477 
 417 
 
 Sept.22 
 
 3 
 
 31 
 
 V 5 
 
 24 
 
 9 
 
 33 
 
 12 
 
 50 
 
 18 
 
 237 
 
 25 
 
 4 
 
 31 
 
 5 
 
 35 
 
 9 
 
 27 
 
 12 
 
 59 
 
 18 
 
 234 
 
 25 
 
 5 
 
 31 
 
 5 
 
 39 
 
 9 
 
 31 
 
 12 
 
 53 
 
 18 
 
 320 
 
 25 
 
 In all, 1,685 "lice" were eaten in 90 days, or 18.7 "lice" per day 
 per larva. The "lice " were of similar average size to those consumed 
 by the lacewing larvae (Table X). It was noticed that before the 
 first molt the ladybird larvae would eat only very small aphides. 
 
 The following is a brief account of the stages of the ashy-gray lady- 
 bird (OUa abdominalis') (PL III). The egg: Yellow, later becoming
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 39 
 
 orange-colored; cylindrical, long oval, slightly tapering to either end, 
 four times as long as broad; deposited in compact masses of from 5 to 
 25 on the leaf, usually on the underside, and with their long axis at 
 right angles to the leaf surf ace ; size, 1.3 by 0.35 mm. The larva: All 
 black at hatching, later with pale markings, becoming more distinct 
 after each successive molt. After the third molt the general color 
 is dark purplish-black, with a median line of pale brick-red spots on 
 the thorax and abdomen and also two lateral rows of similar spots. 
 On segments 1 and 4 of the abdomen occur also two pale spots, one on 
 either side of the median brick-colored spot and midway between it 
 and the corresponding lateral spot. The full-grown larva has a 
 length of 8 millimeters. The pupa: General color white, wing pads 
 sienna brown. A large number of black spots and dashes are present 
 but the prevailing color is white. Average size, 4 by 3.3 mm. The 
 adult: Hemispherical, ashy-gray, with black markings, the elytra 
 sometimes diffused with dull reddish blotches; head black, with 
 central portion white or light gray; thorax (pronotum) black, with 
 gray margins; elytra ashy-gray, with eight black spots on each 
 elytron; legs yellow; abdomen reddish-yellow; average size, 5.2 by 
 4.2 mm. The adults of this species, If confined without food, will 
 devour one another. 
 
 Table XIII indicates the predatory activities of two larvae of 
 Adalia melanopleura on walnut plant lice. 
 
 TABLE XIII. Adalia melanopleura: Predatory activities on. walnut plant lice, Walnut 
 Creek, CaL, 1912. 
 
 
 
 
 Num- 
 
 
 Num- 
 
 
 Num- 
 
 
 
 
 Larva 
 
 Date of 
 
 Date of 
 
 ber 
 "lice" 
 
 Date of 
 
 ber 
 
 "lice" 
 
 Date of 
 
 ber 
 "lice" 
 
 Date of 
 
 Total 
 
 Date of 
 adult 
 
 No. 
 
 hatching. 
 
 molt 1. 
 
 eaten 
 
 molt 2. 
 
 eaten, 
 
 molt 3. 
 
 eaten, 
 
 pupa- 
 
 
 emer- 
 
 
 
 
 to 
 
 
 molts 
 
 
 molts 
 
 tion. 
 
 
 gence. 
 
 
 
 
 molt 1. 
 
 
 Ito2. 
 
 
 2 to 3. 
 
 
 
 
 1 
 2 
 
 Sept. 17 
 
 Sept. 20 
 19 
 
 41 
 
 35 
 
 Sept. 24 
 22 
 
 34 
 
 Sept. 26 
 
 30 
 33 
 
 Sept. 30 
 
 181 
 
 194 
 
 Oct. 12 
 12 
 
 In all, 375 plant lice were eaten in 26 days, or 14.4 per day per larva. 
 The feeding period of both larvae was 13 days as contrasted with an 
 average of practically 18 days for the larvae of the ashy-gray lady- 
 bird. Adalia melanopleura is considerably smaller than that species, 
 its larva consuming in a period of 13 days half as many plant lice 
 as the larva of the larger species will devour in 18 days. This 
 larger species will consume 70 larvae in a single day while the maggot 
 of the large syrphid fly (Cataboniba pyrastri) will dispose of over 100 
 and during the 23 days or so of its existence will devour over 1,000, or 
 about 43.5 lice per day. However, in contrasting the two groups of 
 predaceous insects Syrphidse and Coccinellidae it must be remem- 
 bered that the former are aphidophagous only in the larval state
 
 40 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 while both the adults and larvae of ladybirds feed on plant lice. 
 Mr. E. K. Games, 1 experimenting in the State Insectary at Sacra- 
 mento, Cal., found that 20 adult beetles of Hippodamia convergent 
 averaged 21.8 aphides per day and that the larvae of this species oach 
 consumed from 250 to 300 plant lice during their larval existence. 
 He found that adult females would deposit eggs for from a month to 
 six weeks, laying on the average 15 eggs per day and feeding on the 
 plant lice all the time. Essig 2 states that in the walnut orchards of 
 Ventura County, Cal., OTla dbdominalis, the ashy-gray ladybird, is by 
 far the most beneficial insect in the natural control of the European 
 walnut aphis (ChromapTiis juglandicola) . 
 
 ARTIFICIAL CONTROL OF WALNUT APHIDES. 
 
 The writer has been unable, save in one instance, 3 to find any pub- 
 lished account of artificial control tried or adopted for walnut plant- 
 lice. Until the year 1910 no such work seems to have been performed 
 along this line. 4 In August of that year Mr. P. R. Jones, late of the 
 Bureau of Entomology, carried out a scries of laboratory experiments 
 with a view to determining the efficiency of various washes against 
 these aphides. A small hand pump was fitted with an Eddy-chamber 
 nozzle and the applications made at a medium high pressure. Care 
 was taken that not enough pressure was exerted to kill any of the 
 ''lice" by the force of the spray alone. Examinations were made 10 
 minutes after -the applications. From these experiments the fol- 
 lowing results were obtained: 
 
 Commercial tobacco extract No. 2, containing 40 per cent nicotine, at strengths of 
 1-1,040 to 1-2,048, effective; dilutions weaker than 1-2,048, not effective. 
 
 Commercial tobacco extract No. 1 containing about 4 per cent of nicotine at strength 
 of 1-60, effective; dilutions weaker than 1-60, not effective (1-SO partially effective). 
 
 Commercial tobacco extract No. 1, at strengths varying from 1-60 to 1-200, com- 
 bined with a 3 per cent distillate-oil emulsion, effective. 
 
 Commercial tobacco extract No. 2 at strengths varying from 1-1,000 to 1-2,650 com- 
 bined with a 3 per cent distillate-oil emulsion, effective. 
 
 Commercial tobacco extract No. 1 at strengths "varying from 1-60 to 1-200 combined 
 with a 2 per cent distillate-oil emulsion, effective. 
 
 Commercial tobacco extract No. 2 at strengths varying from 1-1,000 to 1-2,620 com- 
 bined with a 2 per cent distillate-oil emulsion, effective. 
 
 Distillate-oil emulsion at 2, 3, and 4 per cent strengths, effective. 
 
 Commercial lime-sulphur, 1-50, combined with commercial tobacco extract No. 1, 
 1-100, effective. 
 
 Sept., 1912. Carnes, E. K. Insectary Division Reports for the months of June and July, 1912. Mo. 
 Bui. Cal. State Hort. Com., v. 1, no. 10, p. 820-82&. 
 
 Some experiments with the common ladybird ( Hippodamia convergent), p. 821-826. 
 
 Apr., 1912. Essig, E. O. The walnut plant louse ( Chromaphis juglandicola [Kalt] Walker). Mo. BuL 
 Cal. State Com. Hort., v. 1, no. 5, p. 190-194, figs. 72-73. 
 
 Control,?. 192. 
 
 Cf. Biennial Crop Pest and Hort. Report 1911-1912, Oregon Agr. Coll. Exp. Sta. Jan. 10, 1913, p. 165. 
 " Blackleaf 40 " and kerosene emulsion 10 per cent recommended. 
 
 * Since going to press control experiments undertaken in the spring of 1913 In Southern California by 
 the University of California have been published in Circular 107 of tne Agricultural Experiment Station 
 Of the University of California,
 
 Bui. 100, U. S. Dept. of Agriculture. 
 
 PLATE III. 
 
 THE ASHY-GRAY LADYBIRD (,Ou_A ABDOMINALIS). 
 [A, adult; B, eggs; C, larva; D, pupa. (After Essig.)]
 
 j| 100, U. S. Dept of AgriculU 
 
 PLATE IV. 
 
 FIG. 1 .TREE OF THE ROYAL HYBRID WALNUT IN GROVE OF MR. F. LEIB, SAN JOSE, CAL. 
 
 FIG. 2. GENERAL VIEW OF WALNUT GROVE OF MR. F. LEIB, SAN JOSE, CAL.
 
 WALNUT APHIDES IN CALIFORNIA. 41 
 
 Commercial lime-sulphur, 1-50, combined with commercial tobacco extract No. 1, 
 1-200, effective. 
 
 Commercial lime sulphur, 1-70, combined with commercial tobacco extract No. 2, 
 1-1,000, effective. 
 
 Commercial lime-sulphur 1^15, combined with commercial tobacco extract No. 2, 
 1-2,000, effective. 
 
 It is noticeable that the weaker solutions of tobacco extracts were 
 not effective alone, but when combined with distillate-oil emulsion or 
 lime-sulphur proved quite satisfactory. Possibly the most success- 
 ful result was obtained with distillate-oil emulsion of only 2 per cent. 
 Field experiments failed, however, to justify the use of this wash alone, 
 for it proved to lack the killing power found in the tobacco-extract 
 sprays. The emulsion serves, however, as a very good "spreader" 
 for the nicotine killing agent, since it serves to distribute the spray 
 over the leaf surface. Commercial tobacco extract No. 2 proved to 
 have greater insecticidal value than commercial tobacco extract No. 1, 
 judging by the corresponding strengths of the two sprays; and there- 
 fore in the field only the former was used. Foliage tests on an Eastern 
 black walnut tree were made of all the washes used in the laboratory 
 experiments, and in no case was any burning observed to result. This 
 type of walnut seems more susceptible' to burning injury than does 
 the European or so-called "Persian" walnut. 
 
 FIELD EXPERIMENTS. 
 
 SPRING AND SUMMER TREATMENT. 
 
 Experiment No. 1. Lime-sulphur (commercial 1-50) combined with commercial 
 tobacco extract No. 2 (1-1,500). Orchard of Mr. I. Du Bois, San Jose, Cal. Two large 
 European walnut trees badly infested with aphides were sprayed July 1, 1911, under an 
 even pressure of 170 pounds. A count made on the following day showed that 95 per 
 cent of the aphides had been destroyed by the wash. 
 
 Experiment No. 2. Three per cent standard distillate-oil emulsion combined with 
 commercial tobacco extract No. 2 (1-2,000). A large, badly infested European walnut 
 tree in the yard of the experiment station at San Jose was treated, July 3, 1911, with 
 this spray at an even pressure of 170 pounds. A count made July 5 showed that over 
 95 per cent of the aphides had been killed. 
 
 Experiment No. 3. Commercial tobacco extract No. 2 (1-1,500). Orchard of Mr. 
 F. Leib, near San Jose, Cal. (PI. IV, figs. 1, 2). A block of 10 walnut trees badly infested 
 was sprayed, May 21, 1912, under a pressure fluctuating from 60 to 140 pounds. A 
 count made two days later showed that not over 40 per cent of the "lice" were de- 
 stroyed. 
 
 Experiment No. 4- Commercial tobacco extract No. 2 (1-1,500) combined with 2 
 per cent homemade distillate-oil emulsion. Orchard of Mr. F. Leib, near San Jose, 
 Cal. A block of 10 badly infested walnut trees was sprayed, May 21, 1912, under 
 pressure similar to that of experiment No. 3. A count made two days later showed 
 that 98 per cent of the insects had succumbed. Some oil burning appeared on the 
 foliage and nuts owing to insufficient agitation in the preparation of the emulsion 
 and consequent freeing of oil. 
 
 Experiments Nos. 3 and 4 were made to determine whether the tobacco extract 
 alone would prove effective in the field. Results indicate that a weak solution of 
 oil emulsion is necessary to act as a "spreader" for the tobacco.
 
 42 BULLETIN 100, U. S. DEPARTMENT OF AGEICULTUBE. 
 
 Experiment No. 5. Distillate-oil emulsion, 2 per cent. Orchard of Mr. F. Leib, 
 near San Jose, Cal. A block of six badly infested walnut trees was sprayed under 
 110 pounds pressure, July 31, 1912. A count made on August 6 showed that 74 per 
 cent of the "lice" had been destroyed. 
 
 Experiment No. 6. Distillate-oil emulsion, 2 per cent, combined with commercial 
 tobacco extract No. 2 (1-2,000). Orchard of Mr. F. Leib, near San Jose, Cal. (PL 
 IV, figs. 1, 2). Six walnut trees, badly infested, were sprayed under a pressure of 
 110 pounds. A count, made August 6, showed that 85 per cent of the "lice" had 
 been killed by the spray. 
 
 Experiment No. 7, Whale-oil soap, 1 pound; water, 5 gallons. Orchard of Mr. 
 E. I. Hutchinson, Concord, Cal. A block of 12 moderately infested European walnut 
 trees was sprayed under 150 pounds pressure, May 10, 1913. A count made two days 
 later showed that out of 473 "lice" counted, 263, or 55.6 per cent, had been destroyed. 
 A thorough drenching had been applied and the trees were in full leaf. It was noticed 
 that the great majority of the "lice" that escaped were situated close to the base of 
 the midrib. In this position they were partly protected by the projecting rib, and 
 it is to be supposed that the wash lacked the pressure iiece- nry to reach these 
 individuals. 
 
 All the foregoing experiments were undertaken on trees on which 
 the foliage was fully developed. It was noticeable that on thickly 
 foliated trees the percentage of plant lice killed was the smallest, 
 while on thinly foliated trees the greatest mortality resulted. Much 
 of the leaf surface on thickly foliated trees is almost inaccessible 
 to spray. 
 
 A comparison of the results of the foregoing tests favors distillate- 
 oil emulsion and tobacco. The most desirable combination for spring 
 and summer spraying is a 2 per cent distillate-oil emulsion, commer- 
 cial or homemade, combined with commercial tobacco extract No. 
 2, 1 to 1,500. High pressure (150 pounds or over) is desirable, 
 although not absolutely necessary unless the spraying be done before 
 the walnut leaflets have flattened out in spring. 
 
 In tuning the application for the aphides on the leaves it is desirable 
 to spray as early as possible in order to reduce the amount of leaf 
 surface to be covered by the wash and to destroy the plant lice before 
 they attack the nuts. On the other hand it will be found very hard 
 to destroy the plant lice before the leaflets flatten out, for the young 
 leaflets are pressed against one another in a manner that affords 
 very good protection to the insects from a spray. Moreover at this 
 period all the stem-mother plant lice will not have hatched from 
 the winter eggs. The time most preferable for the application is 
 just as soon as the growing leaflets shall have flattened out and before 
 they have attained their full size. At this time the "lice" have all 
 hatched and are all exposed on the underside of the leaves. Should 
 an oil spray be applied care should be taken that there is no free oil 
 in the emulsion, as the young nuts are susceptible to burning. No 
 stronger than a 2 per cent distillate-oil emulsion should be used for 
 this early application. The spray should be directed to the underside 
 of the leaves, and angle nozzles used. A round nozzle is to be pre-
 
 WALNUT APHIDES IN CALIFORNIA. 
 
 ferred to one of the Clipper type, as the former will diffuse the spray 
 better over the leaf surface. Such a driving-spray nozzle as that 
 devised by the Massachusetts Agricultural College is desirable for 
 spraying trees of large size. If there are unsprayed walnut trees 
 in the vicinity it may be necessary to make a second application 
 some two or three weeks later, as plant lice are apt to have migrated 
 from these to the sprayed trees. 
 
 On account of the extended period over which the sexual forms are 
 produced, fall spraying for these forms, unless repeated again and 
 again, will be of little value. 
 
 It should be borne in mind that the number of "lice" hatching in 
 the spring from the winter eggs varies considerably year by year in a 
 given locality or orchard and also that the hatching time of these 
 "lice" is regulated by the sap flow in that particular tree upon which 
 the eggs happened to be placed. The hatching of the winter eggs 
 is not regulated by temperature conditions. Hence the stage in the 
 seasonal development of the aphidids corresponds to the stage in 
 development of that particular tree on which the stem-mother lice 
 were produced, leaving out of consideration the possibility of mi- 
 grants arriving from other trees. This point is of importance when 
 it is considered that the different varieties of cultivated walnuts put 
 out their leaves and produce their nuts at different times and that 
 these functions are performed by individual varieties at different 
 times dependent on locality and seasonal meteorological conditions. 
 
 Table XIV summarizes the control experiments made for spring 
 and summer treatment. 
 
 TABLE XIV. Summary of spring and summer spraying experiments against walnut 
 aphides, San Jose and Walnut Creek, Cal., 1911, 1912, and 1913. 
 
 
 
 
 Result of 
 
 
 Character of spray. 
 
 Date of appli- 
 cation. 
 
 Number 
 
 trees 
 sprayed. 
 
 spray; per 
 cent of 
 plant lice 
 killed. 
 
 Cost per 
 diluted 
 gallon. 
 
 Commercial lime-sulphur, 1-50 and commercial tobacco 
 
 
 
 
 
 extract No 2(11 500) 
 
 July 1,1911 
 
 
 95 
 
 $0.012 
 
 3 per cent distillate-oil emulsion (homemade) and com- 
 mercial tobacco extract No. 2 (1-2,000) 
 
 July 3,1911 
 
 t 
 
 95 
 
 .0088 
 
 Commercial tobacco extract No. 2 (1-1,500) 
 2 per cent distillate-oil emulsion (homemade) and com- 
 
 May 21,1912 
 do 
 
 10 
 10 
 
 40 
 98 
 
 .008 
 .0098 
 
 2 per cent distillate-oil emulsion (commercial) 
 2 per cent distillate-oil emulsion (commercial) and com- 
 mercial tobacco extract No. 2 (1-2,000) 
 
 July 31,1912 
 ....do 
 
 6 
 6 
 
 74 
 
 85 
 
 .0067 
 .0127 
 
 Whale-oil soap (homemade), 1 pound to 5 gallons water.. 
 
 May 10,1913 
 
 12 
 
 55.6 
 
 .004 
 
 WINTER TREATMENT. 
 
 Experiment No. 1. Crude-oil emulsion, 12 per cent (crude oil, 27 Baume'). Orchard 
 of Mr. George Whitman, Concord, Cal. A block of 31 European walnut trees of moder- 
 ate size were sprayed February 25, 1913, under a pressure of from 150 to 175 pounds. 
 Three gallonsof spray were applied to each tree and "Friend" nozzles used. The trees 
 were well drenched. Examination made April 5, 1913, showed that trees were start- 
 ing to leaf. Most of the leaves were as yet tightly closed, but the basal leaves of many
 
 44 BULLETIN 100, U. S. DEPARTMENT OP AGRICULTURE. 
 
 shoots were opened. A general survey of the sprayed block and of a check unsprayed 
 block indicated equal infestation by young stem mothers. Plant lice were not all 
 hatched. An examination made April 15, 1913, showed that trees were well out in 
 leaf. All stem mothers had hatched . A general survey of sprayed and unsprayed 
 trees showed no apparent difference in infestation. A count of 28 leaf clusters selected 
 at random from the sprayed trees yielded 21 stem mothers, while a similar count of 
 the same number of leaf clusters from unsprayed trees yielded 29 stem mothers. It 
 may be inferred from this experiment that the crude-oil emulsion destroyed few, if 
 any, of the winter eggs. 
 
 Experiment No. 2. Commercial lime-sulphur, 1-10. (Concentrated solution, 33 
 Baum6.) Orchard of Mr. George Whitman, Concord, Cal. A block of four large trees 
 of the European walnut were sprayed March 5, 1913, under a pressure of 100 pounds. 
 About 14 gallons of spray were applied to each tree and " Friend" angle nozzles used. 
 Eggs were abundant on both sprayed and check trees. The leaf buds on these trees 
 began to open April 1, 1913. Examination was made April 15, 1913. Trees were then 
 well out in leaf. The stem mothers were all hatched. The lime had no effect in 
 retarding leafing. A count of 20 leaf clusters taken at random on the sprayed block 
 yielded no plant lice, while a similar count of the same number of leaves on the check 
 trees yielded 27 stem mothers. Further examination showed that on the sprayed 
 trees no plant lice could be found, while on the check trees nearly every leaf cluster 
 had one or more of the insects. 
 
 A subsidiary experiment was undertaken on two young California black walnut 
 trees, both infested with eggs. One of these trees was treated with commercial lime- 
 sulphur, 1-9 (concentrated solution 33 Baum6), and the other left as a check. On 
 the sprayed tree no eggs hatched and when examined on April 17, 1913, the eggs were 
 shrunken and distorted, the embryos having been destroyed within the eggshell. 
 The eggs on the check tree hatched normally about the end of March. 
 
 Experiment No. S. Crude-oil emulsion, lime-sulphur, and "Yel- 
 ros." Vrooman orchard, Santa Rosa, Cal. Four plats were 
 sprayed, April 9-11, 1913, with a power outfit at high pressure, as 
 follows: Plat 1, 40 trees, crude oil (22 Baume") emulsion, 8 per cent; 
 plat 2, 40 trees, lime-sulphur, 1 to 8; plat 3, "Yel-ros," 1 to 25, 
 16 trees; plat 4, "Yel-ros," 1 to 40, 24 trees. These applications 
 were made on late Franquette walnuts, dormant at the time of spray- 
 ing. The orchard was well infested with the winter eggs of the plant 
 lice. An examination, May 27, 1913, showed that the trees were well 
 out in leaf. Stem mother plant lice were mostly about two-thirds 
 grown. Counts of 80 leaves (about 480 leaflets) taken at random 
 from each of the four plats and from a check unsprayed plat resulted 
 as follows: 
 
 TABLE XV. Winter spraying experiment No. S against walnut aphides, 
 orchard, Santa Rosa, Cal., 1913. 
 
 Vrooman 
 
 
 Number of 
 
 Percent 
 
 Plat. 
 
 "lice" on 
 
 of number 
 
 
 80 leaves. 
 
 on check. 
 
 Crude-oil emulsion, 8 per cent 
 
 11 
 
 10.6 
 
 Lime-sulphur. 1 to 8. 
 
 2 
 
 1.9 
 
 " Yel-ros " 1 to 25 
 
 14 
 
 13.4 
 
 "Yel-ros " 1 to 40 
 
 97 
 
 93 2 
 
 Check unsprayed . ... 
 
 104 
 
 100.0 
 
 

 
 WALNUT APHIDES IN CALIFORNIA. 
 
 45 
 
 The best results, therefore, were obtained by the lime-sulphur 
 wash. The greater efficiency of the 8 per cent crude-oil emulsion 
 over the 12 per cent crude oil used in experiment No. 1 is probably 
 due to the heavier grade of oil (22 Baume") used in the 8 per cent 
 experiment. The heavier oil remains longer on the trees and coats 
 the eggs of the aphides more satisfactorily than the oil of lighter 
 grade. As may be seen from Table XVI both the 8 per cent crude- 
 oil emulsion and " Yel-ros," 1 to 25, gave good results, but " Yel-ros," 
 1 to 40, was quite ineffective. Table XVI is a summary of experiments 
 against the winter eggs: 
 
 TABLE XVI. Summary of experiments on the winter eggs, Walnut Creek and Santa 
 Rosa, Cal, 1913. 
 
 
 
 
 
 Plant 
 
 
 Character of spray. 
 
 Date of ap- 
 plication. 
 
 Number 
 of trees 
 sprayed. 
 
 Date of ex- 
 amination. 
 
 lice 
 present 
 (check 
 
 Cost per 
 diluted 
 gallon. 
 
 
 
 
 
 100). 
 
 
 
 
 
 
 Per cent. 
 
 
 Crude-oil (27 Baume 1 ) emulsion, 12 per cent 
 
 Feb. 25.... 
 Mar 5 
 
 31 
 4 
 
 Apr. 5, 15. . 
 do 
 
 72.4 
 
 
 J0.01 
 02 
 
 Crude-oil (22 Baum6) emulsion, 8 per cent 
 Commercial lime-sulphur, 1 to 8 
 
 Apr. 9-11.. 
 do 
 
 40 
 40 
 
 May 27.... 
 do 
 
 10.6 
 1.9 
 
 .0073 
 .025- 
 
 "Yel-ros " 1 to 25 
 
 do 
 
 16 
 
 do 
 
 13 4 
 
 028 
 
 "Yel-ros," 1 to 40 . . 
 
 do.... 
 
 24 
 
 do.... 
 
 93.2 
 
 .0175 
 
 
 
 
 
 
 
 It is in a measure unfortunate that the homemade 1-2-1 lime- 
 sulphur spray was not tried. This is considerably cheaper than the 
 commercial article, but there is no reason to suppose that the winter 
 formula of the homemade lime-sulphur would not prove quite effective 
 judging by the results obtained with commercial lime-sulphur. 
 
 In recommending winter sprays for the plant lice infesting walnut 
 trees the writer must accord the preference to lime-sulphur, 1-8 to 
 1-11, while good work may be expected from crude-oil emulsion, 8 to 
 12 per cent, using the heavier grades of oil (not lighter than 24 
 Baume), and from " Yel-ros," 1-25. The oil emulsion (homemade) is 
 the cheapest winter spray, although there is li ttle difference between its 
 cost and that of the homemade lime-sulphur wash, winter formula. 
 
 In applying the spray for the aphis eggs the wash should be directed 
 so as to cover completely every part of the twigs and limbs. Late 
 spraying, i. e., making the application just before the buds are begin- 
 ning to swell, is preferable to spraying earlier, especially if crude-oil 
 emulsion is used, as the oil does its best work soon after it is applied 
 and the plant lice at hatching time are more easily destroyed by it. 
 
 In concluding the section on artificial control the author would like 
 to express his thanks to Mr. Frank Leib, San Jose, Cal., and Messrs. 
 George Whitman and E. I. Hutchinson, Concord, Cal., for their help and 
 cooperation in the carrying out of field experiments on their orchards, 
 and also to Balfour, Guthrie & Co., San Francisco, Cal., by whose 
 courtesy the Santa Rosa experiments were made possible, they having 
 made the spray applications under the author's supervision.
 
 46 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 SUMMARY. 
 
 The life history of walnut aphides in California is briefly as follows: 
 A week or so before the buds open on the trees in the spring the 
 aphiclids begin to hatch from the winter eggs. As soon as the young 
 foliage appears the "lice" settle on it, and after feeding for a month 
 or so become adults. These stem mothers are always winged and like 
 plant lice of later generations are capable of migrating to other trees 
 and orchards. As soon as they are fully developed they produce 
 young parthenogenetically. These second-generation young become 
 mature in three weeks and in turn produce young. The individuals 
 of the third and subsequent generations of summer mature in about 
 16 days. On early-leafing varieties there are 10 or 11 viviparous 
 generations in the year while on late varieties there are 8 or 9. The 
 production of the sexual generation is prolonged over four months, 
 these forms first appearing in July. After the sexes (comprised of 
 the winged male and the wingless female) mate, the female repairs to 
 the twigs and limbs of the tree, there to deposit her eggs. Winter is 
 passed in the egg stage only. 
 
 In general the aphidids inhabit the underside of the leaves, but those 
 of the second, third, and fourth generations often attack the nuts, 
 sometimes seriously dwarfing them (see PI. I, fig. 1). Occasionally 
 the "lice" will be found on the upper surface of the leaf. When infes- 
 tation on the leaves and nuts is severe the vitality of the infested tree 
 is impaired. The aphidids excrete a sweet, gummy, transparent sub- 
 stance much sought after by ants, and in this thrives a black sooty 
 fungus. This black fungus often covers the upper sides of the lower 
 leaves and the upper part of the nuts, thereby interfering with the 
 respiratory action of the plant tissues. 
 
 Walnut plant lice have many natural foes, all predatory. These 
 serve to keep the aphidids in check but do not appear in sufficient 
 numbers until after the "lice" have had time to injure the nuts. The 
 most persistent of them is the ashy-gray ladybird beetle (Olla abdom- 
 indLis Say). 
 
 Aphidids on walnuts can be controlled artificially with sprays. The 
 winter spraying directed against the eggs is the easier to apply, and high 
 trees can be reached by a winter wash with ease, whereas in the spring 
 and summer so thick is the foliage that a thorough application is hard 
 to accomplish satisfactorily. Furthermore, far less material is 
 required when the trees are bare. Lime-sulphur and crude-oil emul- 
 sions are effective, especially the first named. The spray should be 
 directed all over limbs and twigs so as to cover every part. If it 
 is necessary to spray in spring or summer, a combination of 2 per cent 
 distillate-oil emulsion and commercial tobacco extract No. 2 (1 to 
 1,500) will prove effective provided it be applied under a pressure of 
 at least 150 pounds and the spray directed on the nuts and underside 
 of the leaves.
 
 WALNUT APHIDES IN CALIFORNIA. 47 
 
 BIBLIOGRAPHY. 
 
 CHROMAPHIS JUGLANDICOLA Kaltenbach. 
 
 1843. Kaltenbach, J. H. Monographic der Familieii der Pflanzenlause . . . Aachen, 
 1843. 
 
 "Lachnusjufflandicola." Original description, with colored figures. 
 
 1857. Koch, C. L. Die Pflanzenlause Aphiden, Niirnberg, 1854-1857. 
 
 " Callipterus jugland icola Koch," p. 224, fig. 297, 1857. Description and colored figures. 
 1860. Passerini, Carlo. Gli Afidi, Parma, 1860. 
 
 " Callipterus juglandicola Kalt." recorded. 
 
 1870. Walker, Francis. Notes on aphides. Zoologist, ser. 2, v. 5, pp. 1996-2001, 
 Feb., 1870. 
 
 " Callipterus -juglandis," p. 2000; Callaphis proposed, p. 2000. " Chromaphis peglandicola," 
 p. 2001. Genus Chromaphis erected. 
 
 1881. Buckton, G. W. Monograph of the British Aphides, v. 3, London, 1881. 
 "Pterocallis juglandicola Kalt.," p. 32-34. Description and colored plate. 
 
 1906. Schouteden, H. Catalogue des Aphides de Belgique. Mem. Soc. Ent. Belg., 
 v. 12, pp. 189-246. 
 
 " Callipterus juglandicola Kalt.," p. 209-210. Recorded. 
 
 1909. Essig, E. O. Aphididae of southern California, II. Pomona Col. Jour. Ent., 
 
 v. 1, no. 2, pp. 47-52, June, 1909. 
 " Callipterus juglandicola Koch," p. 51-52. Description and figures. 
 
 1910. Gillette, C. P. Plant-louse notes, family Aphididse (continued). Jour. Econ. 
 
 Ent., v. 3, no. 4, pp. 367-371, pi. 24. 
 
 " Chromaphis juglandicola," p. 367, fig. 4. Note of occurrence and figure of antenna of 
 winged female. 
 
 1910. Wilson, H. F. A key to the genera and notes on the synonymy of the tribe 
 Callipterini, family Aphididse. Canad. Ent., v. 42, no. 8, pp. 253-259, 
 Aug., 1910. 
 
 " Chromaphis juglandicola Kalt.," pp. 257-258. Refers to Walker's erection of the genus 
 Chromaphis. 
 
 1912. Essig, E. 0. The walnut plant louse (Chromaphis juglandicola (Kalt.) Walker). 
 
 Mo. Bui. Cal. State Com. Hort., v. 1, no. 5, pp. 190-194, figs. 72-73, April, 
 1912. 
 
 Description and figures, natural control notes. 
 
 1913. Wilson, H. F., and Lovett, A. L. Miscellaneous insect pests of orchard and 
 
 garden. Bien. Crop Pest and Hort. Rpt. 1911-12, Oregon Agr. Col. Expt. 
 Sta., pp. 147-165. 
 
 " Chromaphis juglandicola Kalt.," p. 165. Note of occurrence and remedies. 
 
 MONELLIA CARY^E Monell. 
 
 1879. Monell, J. Notes on the Aphididse of the United States, Part II. Notes on 
 Aphididse, with descriptions of new species. U. S. Geol. and Geog. Sur- 
 vey Bui. 5, no. 1, pp. 18-32, Jan. 22, 1879. 
 
 " Callipterus caryse, n. sp.," p. 31. Original description. 
 
 1879. Thomas, Cyrus. Eighth Report of the State Entomologist on the Noxious and 
 Beneficial Insects of the State of Illinois, Springfield, 1879. 
 " Callipterus caryx, n. sp.," p. 199. Note of occurrence.
 
 48 BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
 
 1910. Williams, T. A. The Aphididaj of Nebraska. Nebr. Univ. Studies, v. 10 
 no. 2, pp. 85-175, April, 1910. 
 
 " Cattipterus caryx Monell," p. 115. Description and note of occurrence. 
 
 1910. Gillette, C. P. Plant-louse notes, family Aphididse (continued), pi. 24. Jour. 
 Econ. Ent., v. 3, no. 4, pp. 367-371, Aug., 1910. 
 "Monellia caryx," p. 367. Note of occurrence and figure. 
 
 1910. Davis, J. J. A list of the Aphididse of Illinois, with notes on some of the 
 species. Jour. Econ. Ent., v. 3, no. 5, p. 407^120, Oct., 1910. 
 " Callipterus caryx Monl.," p. 417. Note of occurrence. 
 
 MONELLIA CARYELLA Fitch. 
 
 1855. Fitch, Asa. First Report on the Noxious, Beneficial, and other Insects of 
 
 the State of New York, Albany, 1855. 
 
 "Aphis caryella Fitch," pp. 163-165. Original description. 
 
 1856. Fitch, Asa. Third Report on the Noxious and other Insects of the State of 
 
 New York, Albany, 1856. 
 
 "Hickory gay-louse, Callipterus caryeUus Fitch," pp. 448-449. Short description. 
 
 1862. Walsh, B. D. On the genera of Aphididse found in the United States. Proc. 
 Ent. Soc. Phila., v. 1, pp. 294-311. 
 
 " Callipterus caryellus Fitch," p. 302. Reference. 
 
 1879. Thomas, Cyrus. Eighth Report of the State Entomologist on the Noxious 
 and Beneficial Insects of the State of Illinois, Springfield, 1879. 
 " Callipterus caryellus FiJ^h," pp. 170-171. Note of occurrence. 
 
 1887. Oestlund, O. W. Synopsis of the Aphididae of Minnesota. Geol. and Nat. 
 Hist. Survey Minn. Bui. 4. 
 
 " Monellia caryella Fitch," p. 45. Genus Monellia erected . Note of occurrence. 
 
 1910. Davis, J. J. A list of the Aphididse of Illinois, with notes on some of the spe- 
 cies. Jour. Econ. Ent., v. 3, no. 5, pp. 407-420. 
 "Monellia caryella Fitch," p. 419. 
 
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