UNIVERSITY OF CALIFORNIA PUBLICATIONS. COLLEGE OF AGRICULTURE. AGRICULTURAL EXPERIMENT STATION, BERKELEY, ( JA LIFORNIA. THE GRAPE LEAF-HOPPER. By H. J. QUAYLE. BULLETIN No. 198. (Berkeley, Cal., July, 1908.) SACRAMENTO: w. Wj shannon, : : : : superintendent state printing 1908. BENJAMIN IDE WHEELER, Ph.D., LL.D., President of the University. EXPERIMENT STATION STAFF. E. J. WICKSON, M.A., Director and Horticulturist. E. W. HILGARD, Ph.D., LL.D., Chemist. W. A. SETCHELL, Ph.D., Botanist. EL WOOD MEAD, M.S., C.E., Irrigation Engineer. (Absent on leave.) LEROY ANDERSON, Ph.D., Dairy Industry and Superintendent University Farm. M. E. JAFFA, M.S., Nutrition Expert, in charge of the Poultry Station. C. W. WOOD WORTH, M.S., Entomologist. R. H. LOUGHRIDGE, Ph.D., Soil Chemist and Physicist. G. W. SHAW, M.A., Ph.D., Agricultural Technologist, in charge of Cereal Stations. GEORGE E. COLBY, M.S., Chemist, in charge of Agricultural Chemical Laboratory. RALPH E. SMITH, B.S., Plant Pathologist and Superintendent of Southern California Pathological Laboratory and Experiment Station. Whittier. A. R. WARD, B.S.A., D.V.M., Veterinarian and Bacteriologist. E. W. MAJOR, B.Agr., Animal Industry. H. M. HALL, M.S., Assistant Botanist. H. J. QUAYLE, A.B., Assistant Entomologist. Whittier. W. T. CLARKE, B.S., Assistant Horticulturist and Superintendent of University Extension in Agriculture. JOHN S. BURD, B.S., Chemist, in charge of Fertilizer Control. C. M. HARING, D.V.M., Assistant Veterinarian and Bacteriologist. H. A. HOPPER, B.S.A., Assistant in Dairy Husbandry. J. H. NORTON, M.S., Assistant Chemist in charge Fertilizer) „ Experiments, I Citrus Experiment T. F. HUNT, B.S., Assistant Horticulturist, ) Station, Riverside. E. B. BABCOCK, B.S., Assistant Plant Pathologist. E. H. SMITH, M.S., Assistant Plant Pathologist. F. L. YEAW, B.S., Assistant Plant Pathologist. H. J. RAMSEY, M.S., Assistant Plant Pathologist, ) Southern California Patholog- C. O. SMITH, M.S., " " " ) ical Laboratory, Whittier. R. E. MANSELL, Assistant in Horticulture, in charge of Central Station Grounds. RALPH BENTON, B.S., B.L., Assistant in Entomology (Apiculture) . A. J. GAUMNITZ, M.S., Assistant in Cereal Investigations. RACHAEL CORR, M.A., Assistant in Cereal Laboratory. HANS C. HOLM, B.S., Assistant in Zymology. P. L. McCREARY, B.S., Laboratory Assistant in Fertilizer Control. F. E. JOHNSON, B. L., Assistant in Soil Laboratory. M. E. STOVER, B.S., Assistant in Agricultural Chemical Laboratory. D. R. HOAGLAND, A.B., Assistant in Agricultural Chemical Laboratory. CHARLES FUCHS, Curator Entomological Museum. P. L. HIBBARD, B.S., Assistant Fertilizer Control Laboratory. M. E. SHERWIN, Field Assistant in Agronomy. W. H. VOLCK, Field Assistant in Entomology. Watsonville. E. L. MORRIS, B.S., Field Assistant in Entomology. San Jose. J. S. HUNTER, Field Assistant in Entomology. San Mateo. D. L. BUNNELL, Clerk to the Director. JOHN TUOHY, Patron, J Tulare Suhstation) Tulare . J. T. BEARSS, Foreman, ) J. W. ROPER, Patron, ) E. C. MILLER, In charge, ) ROY JONES, Patron, ) N. D. INGHAM, Foreman, j VINCENT J. HUNTLEY, Foreman of California Poultry Experiment Station, Petaluma. University Forestry Station, Chico. University Forestry Station, Santa Monica. The Station publications (Reports and Bulletins), so long as avail- able, will be sent to any citizen of the State on application. OUTLINE. Page. GENERAL CONSIDERATIONS 177 Early accounts ; Destructiveness ; Distribution, general, local. LIFE HISTORY AND HABITS 181 Overwintering Adults 181 Food habits ; Relation of food to development and activity ; Influence of temperature upon activity ; Proportion of the sexes ; Migrations ; Time they attack the vine ; Do they feed exclusively on the vine ; Habits on the vine ; Copulation and oviposition. The Egg * 186 Description and appearance ; Wnere laid ; Number ; Rate of egg laying ; Incubation period ; Percentage of eggs that hatch ; Effect of oviposition upon the leaf. The Nymph 192 The hatching process ; First stage ; Second stage ; Third stage ; Fourth stage ; Fifth stage ; Moulting ; Habits of feeding ; Transfer to other food plants. The Adult 196 Time of reaching maturity ; Feeding habits ; Copulation and oviposition ; Activity and migrations ; Activity of the sexes ; Proportion of the sexes ; Differences in coloring ; The varieties of the species comes ; Proportion of the varieties ; Common name of the insect ; Preferences for different varieties of vines. Development 200 Length of life cycles ; Number of generations ; Comparisons of development in other localities. NATURAL CONTROL 202 Climatic ; Parasitic ; Predatory ; Fungous. MECHANICAL CONTROL 203 Blowers and suction ; Torches ; Dry powders ; Sticky shields ; Fumigation ; Sprays and washes ; Screens or cages. FARM PRACTICES 214 Plowing ; Sheeping. SUMMARY 215 LITERATURE 217 THE GRAPE LEAF-HOPPER (Typhlocyba comes Say.) By H. J. QUAYLE. GENERAL CONSIDERATIONS. Early Accounts. — The grape leaf-hopper was first named and described by Thomas Say 1 in the year 1825. Specimens were taken Fig. 1. Grape leaf' showing first indication of injury due to hoppers. The white specks represent where the insects have been feeding. that year from Missouri, and three or four years later it was reported as an important pest of the vine in Massachusetts. Harris 2 in 1841 wrote the first complete account of the insect and fully appreciated 1 Jour. Acad, of Nat. Sciences. Phil. iv. 327. 2 Harris. Ins. Inj. to Vegetation, Flint Ed., 227. 178 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. the injury caused by it, and ever since that time it has occupied a very important place in the literature of grape insects in this country. Harris's account of the insect remained the standard for a long while, and no very thorough work was done on the life history of the insect until it was undertaken by Slingerland in 1901. 1 In California it has been reported as a pest of the vine since 1875. The accounts of insects in the "Pacific Rural Press" furnish a fairly good index on the occurrence of injurious species in this State, and the first account there given is in the issue of April 12, 1879. Notices regarding this insect have appeared frequently in Fig. 2. Young grape leaves in advanced stage of hopper injury. These leaves had completely dried up and fallen to the ground in the early spring. Photographed April 20, 1907. the press of the State, as well as other publications, since that time. Brief notices of its occurrence have been printed in the State Horti- cultural Commission reports, and a bulletin on the insect was issued from this station in 1897. 2 Destructiveness. — With the exception of the phylloxera, the vine hopper is undoubtedly the most destructive insect pest of the vine in the State. It is more uniformly present than any other insect 1 Slingerland, Cornell Exp. Sta. Bull. 215, •Woodworth, Cal. Agr. Exp. Sia. Bull. 116. Bulletin 198. THE GRAPE LEAF-HOPPER. 179 attacking the vine, and each year in some parts of the State it occurs in very great numbers, and in such sections, it levies a heavy tax upon the vineyard interests. To give expression to this loss in money value, for example, in one vineyard of about a thousand acres near Madera, the owner estimated that the damage done last year by hoppers would aggregate about $10,000. The grape leaf-hopper belongs to the class of injurious insects that obtain their food by sucking the juices from the plant. Scale insects and plant lice are other well known pests belonging to this same general group, which obtain their food in much the same way that the mosquito sucks our blood. The sharp pointed beak or proboscis of the hopper (Fig. 4) is thrust into the tissues of the grape leaf and the liquid parts extract- ed therefrom. The feeding is done mostly on the un- derside of the leaf, and those leaves around the base of the vine are the ones first attacked. The first indica- tion of their work is a mottled appear- ance of the leaf due to the pale spots formed wherever the beak has been in- serted and the green parts taken out (Fig. 1). As the feeding continues these spots become more numerous, and this pale yellow color spreads over the entire surface; and finally the leaf turns brown and drops off (Fig. 2). This injury has been observed as early as April or May, and thus the vine from the very beginning of the season is prevented from making its normal growth. As the hoppers increase in numbers the injury increases with the advancement of the season. In midsummer quite a large area about the crown of the vine will show all the leaves pale colored or completely dried up, and, in severe cases, the entire vine is thus affected. This drying up and dropping off of the leaves allows the sun to have free access to the fruit and may cause sunburn. We have seen the fruit thus exposed and badly sunburned as early as the middle of June. The falling off of the leaves prematurely also pre- Fig. 3. The foliage and fruit of the grape is often badly- smutted by the excrement of hoppers. The black specks on the above leaf indicate this. 180 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. labium vents the berry from maturing properly since it is in the leaves of the plant that the sugar of the berry is manufactured. The grape thus loses much of its flavor and sweetness, and likewise the char- acteristic coloring, which is so desirable in certain table varieties, is not attained. The fruit, furthermore, is badly smutted by the exuda- tions of the insects, and this serves as a harboring place for the collection of dust and dirt, and for the growth of fungi (Fig. 3). The dropping of the leaves or any interference with their normal func- tions likewise has its effect on the growth of the wood of the vine. The canes fail to ripen normally for the next year's wood, and many of the buds fail to develop in the following spring. The vine may thus be more or less permanently stunted in growth, and even killed in severe cases of Wan dibits grape leaf -hopper injury. Distribution; General. — The grape leaf -hopper {Typhlocyba comes Say) is a widely distributed native Ameri- can insect occurring in the United States practically wherever the vine is grown. It is frequently notably in- jurious in the grape belts of New York and Ohio, as well as other less important grape sections in this country. In Europe this species is replaced by two other related species, Typhlocyba flavescens and Typhlocyba viticola. The former seems to be the more injurious of the two and occurs throughout all of temperate Europe and northern Africa, while the latter is confined mostly to Italy and the neighboring islands. 1 Local. — In California our species is found in practically all of the vine growing sections, but is most injurious in the Sacramento and San Joaquin valleys. In the coast valleys another larger species (Tettegonia atropunctata) is frequently injurious, most commonly during the earlier part of the season. This species appears not to feed exclusively on the vine, and during midsummer and later is •U\ Fig. 4. The beak, or mouth-parts, of the grape leaf-hopper. Much en- larged. Mayet's Insectes do la Vigne, 168. Bulletin 198. the GRAPE LEAF-HOPPER. 181 distributed over other food plants. During 1907 the grape leaf-hopper was particularly abundant in many of the vineyards about Fresno, and also in the lower part of the San Joaquin Valley around Lodi. LIFE HISTORY AND HABITS. OVERWINTERING ADULTS. During the colder weather of winter the hoppers may be found in large numbers in the leaves or rubbish in the vineyard, or along the bordering roadsides and fences. Where leaves have been blown together in bunches or lodged in weeds or grass over the vineyard or its borders, hoppers will be especially likely to be present during the colder or wet rainy days of the winter season. They will also be found harbor- ing low down along the fences or in the weeds or other growth among the vines. Alfilaria, one of the commonest plants in many California vineyards in winter, forms a close rosette on the ground, and hoppers will be found abundantly under the low spreading foliage of this plant. Food Habits. — The grape leaf -hopper feeds on a large variety of plants during the winter season. It will be found feeding chiefly during the warmer days of winter, and resting more or less dormant during the colder or rainy weather. It attacks practically everything that may be growing in the vineyard or vicinity, although a preference is shown for certain plants. Alfilaria is readily attacked by these insects, and where hoppers are numerous the foliage of this plant will be seen to have a pale yellow color as a result of their work. The low spreading foliage seems to offer suitable conditions for the hoppers when they are not feeding, so that they will be found on the underside of these plants almost continuously, regardless of the kind of weather. Burr clover is also readily attacked by the hoppers in winter, as well as rag weed, dock, wild mustard, alfalfa, and several kinds of grains and grasses. They show a preference, however, for such plants as the alfilaria and the clovers as against the grains and grasses. The hoppers that were taken into the laboratory in the early spring invariably died in the course of two or three days if deprived of food. Under the same conditions they were easily maintained upon alfilaria or other food. They were confined in lantern globes which were placed in the open window of the laboratory, so that the conditions as regards temperature and moisture were not very different from that of the vineyard. Hoppers were also confined in lantern globes in the vineyard, but in all cases they died very soon without food, though the more dormant they were the longer they were able to survive. 182 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Many of the hoppers succumbed to long continued wet weather or other unusual conditions in winter. After about two weeks of almost continuous rain we have counted as many as 700 dead hoppers under a single bunch of alfilaria. This mortality may be partly accounted for because of unsuitable conditions for obtaining food, though the direct effect of exposure to such conditions is probably the more important factor. Relation of Food to Development and Activity. — The activity of the insects is dependent primarily upon food and temperature, and the latter largely influences the former. No matter how much nutritious food may be available, if the temperature is sufficiently low they become dormant and are revived only upon the rise of temperature ; but once they become active through the influence of a higher temperature, they require food to maintain their activity. Influence of Temperature upon Activity. — On the warm days of winter the hoppers are very active and fly up in large numbers before a person as he walks through the vineyard. On the contrary, on a cold or wet day they may only be disturbed by actually moving the object upon which they are resting, and then they will fly but a very short distance, — not more than a foot or two generally. It is possible during such days to pick up the leaves, with a dozen or more hoppers resting on the under surface, and place them in a cyanide bottle without disturbing them. They are most active during the warmer portions of the day, — from nine or ten o'clock in the morning, when the dew is dried from the leaves, until three or four in the afternoon. Experiments carried on in the laboratory to determine the effect of temperature on overwintering adults indicated that a temperature of 110° F. was nearly always fatal. These experiments consisted in con- fining the hoppers in a double glass vial and heating gradually with artificial heat. A small homo vial was contained within a larger one, and a thermometer extended through the corks of both vials so that the bulb was contained in the center of the inner vial with the hoppers. Cotton was placed in the bottom of this vial to prevent them from coming in contact with the glass when they would fall down. The whole apparatus prevented so far as possible the unequal heating of the sides of the vial as compared with the air in the interior. In some of the experiments, as given in the table below, the tem- perature was first reduced by ice and salt to 30° F. or lower, and suddenly raised again to a point at which all the insects were killed. By consulting the table it will be seen that they became dormant at 60 to 65°P. and revived again at about 70°F. At 80° to 90°F. the first Bulletin 198. THE GRAPE LEAF-HOPPER. 183 of them would be killed by the heat. The optimum temperature under these conditions was between 70° and 85°F. The temperature of the room during the experiments was between 65° and 75 °F. In most of the experiments it was the ordinary air of the room, as regards humidity, but in some a moist plug of cotton was contained in the vial with the insects, and thus the humidity was considerably increased. The experiments in detail are tabulated below: Temperature Experiments. Date. __ X CD B CD 05 -» a E- B ►d o CD o P ?s • B a P a < CB P *_ O __ B^ <° CD P C_t3 O CD < CO P CO CD Pi F SB CO o CD p pi p CD P <-i CD i° CD >-h 13 rt __ : x 1907— March 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 7 8 8 8 8 8 8 8 8 7 6 6 6 6 10 6 7 8 66 66 70 72 72 72 72 72 70 68 70 70 70 70 70 72 72 72 O o o o 85 90 95 95 100 110* 105* 100* 100 105 87 86 84 80 84 105 100 105 lfo 110 110 110 110 120 115 110 110 110 102 94 110 114 102 120 110 110 3m March 20 ________ 4 March 20 10 March 20 _ _ 6 March 20 5 March 20 5 March 20 6 March 20 8 March 23 - _ 50 60 65 65-60 66 60 62 50-40 50-45 60-50 62-55 64-56 60-54 30 45 35 25 30 40 28t 70 70 76 74-8 64-72 57-66 65-72 15 March 23 _ _ 12 March 23 10 March 23 13 March 23 11 March 23 15 March 23 .. 20 March 23 March 23 March 23 _ Vial kept moist by wet plug cotton. tHeld for 10 m. In the column ' ' Inactive at " is indicated when the hoppers ceased moving about, and in the column ' ' Active at ' ' when they first regained their locomotive powers. The general conclusions suggested by these experiments are as follows: A rise in temperature to 110°F., and in one or two cases to 120°F., invariably killed the hoppers. "With moisture in the tube they appeared to withstand a slightly higher temperature. Cold to as low as 25 °F. had no effect upon them except to make them temporarily dormant. When they were subjected again to the higher temperature they were killed the same as if started from the room temperature, except, apparently, to make the first succumb at a lower temperature. The practical bearing of these experiments can hardly be interpreted beyond the fact that a sudden rise in temperature may be fatal to some of the insects. In this the rather unnatural condition of dry, artificial heat must also be taken into consideration. 184 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Proportion of the Sexes of Overwintering Hoppers. Collected. Number of Specimens Examined. Females. Males. ' Percentage Females. Percentage Males. March 6th _ 1,500 130 272 127 134 675 65 175 72. 100 825 65 97 55 34 45 50 64.4 57 74.6 55 March 28th _. 50 April 12th April 19th April 29th . 35.6 43 25.4 Totals and av. percentage- 2,163 1,087 1,076 50.26 49.74 Fig. 5. Tip of abdomen of female grape leaf-hopper, showing ovipositor. The black tipped appendages, the cerci, obscure the other parts of the ovipositor shown in Fig. 6 below. Greatly enlarged. It will be seen from the average percentage in the above table that there is practically no difference between the numbers of the sexes, so that we may con- clude that both sexes are able to withstand the winter conditions equally well. Migrations. — When plowing is begun in the vineyard in the spring, before the foliage appears on the vine, the food supply — consisting of what- ever vegetation may be growing — is turned under and most of the hoppers are obliged to look elsewhere for food. Some of the insects remain in the vineyard and subsist upon what little growth may be left by the plow. The larger number, however, must look elsewhere for food, and this is generally found in the immediate vicinity, usually around the borders of the vineyard. We have seen all the vegetation growing along the roadsides of badly infested vineyards completely deprived of the green coloring matter. After the vineyard was plowed the hoppers continued to feed here, largely, until the vines came into leaf, when they migrated back into the vineyards. These are the only distinct movements we have observed with the overwintering hoppers in the spring. Time they Attack the Vine. — The first observed feeding on the grape foliage at Lodi during 1907 was March 28th, on an' old Mission vine- yard that was considerably in advance of the other surrounding vine- yards. A week or two later, however, the foliage in many vineyards was far enough along to attract a good many of the hoppers from their Bulletin 198. THE GRAPE LEAF-HOPPER. 185 varied winter food plants. In 1908 an occasional hopper was found on vines in the Sonoma Valley as early as March 18th. Do they Feed Exclusively on the Vinef — Once they begin to feed upon the vine they do not leave it for other food unless, of course, they incidentally happen to find themselves in other situations. During two or three weeks while the vine is coming into foliage, some hoppers may be found on the vine and others on the winter food plants, but those that are still feeding on the other vegeta- tion have not yet found their way to the vines. It may be a couple of weeks after the first foliage appears, therefore, before all the hoppers will be found on the vine; but, once they begin to feed on the grape, they remain until the vine becomes dormant at the end of the season. Fig. 6. The two pairs of valves of the ovipositor with which the insect inserts its egg into the leaf tissues. Greatly enlarged. Habits on the Vine. — While the leaves are still expanding and not yet affording much protection the hoppers will be found most commonly „ on the concave side of the leaves that are not yet fully expanded, or on the leaves near the base of the vine, where they are not so completely exposed. At this period they were not observed to move about to any extent, and seemed to be pretty well occupied with feeding". Copulation and Oviposition. — On April 30, 1907, they were observed pairing for the first time. This was approximately three weeks after they had begun to feed upon the vines. The first eggs were seen in the leaves on May 4th, and from this date on the hoppers were laying eggs almost continuously. Egg laying occurs then just about one month after feeding begins on the vine. The eggs are remarkably well tucked away in the leaf tissues by means of a sharp lance-like ovipositor, as shown in figures 5 and 6. Fig. 7. grape Tip of abdomen leaf-hopper. Much 186 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. THE EGG. Description and Appearance. — The eggs of the grape leaf -hopper are very minute objects about three hundredths of an inch long and about one third as wide. They are slightly bean-shaped, as shown in figures 8 and 9. As they are situated naturally in the leaf, within the tissues, they are difficult to detect unless one is familiar with their appearance. If the light is at the right angle the epidermis will be seen to be raised and slightly more transparent than the surrounding tissue, and the form of the egg distinguished beneath. "We occasionally met growers who claimed to have observed the eggs on the underside of the leaf; but they were mistaken in thinking that little transparent droplets of sap were the eggs of the hopper. These are exuda- tions of sap which usually occur along the larger veins, and do resemble somewhat an insect egg. The outer surface of these droplets of sap soon hard- ens or becomes viscid on exposure to the air, thus resembling the shell of an egg and making the simi- larity more complete. Where Laid. — Harris, 1 in 1841, stated that the eggs of the hopper were laid on the leaves, but this statement appears not to have been substantiated by actual observation. Townsend 2 in 1891 supposed that the drops of sap, mentioned above, represented the egg punctures of these insects, but this is now known to be erroneous. Marlatt 3 in 1895 stated that "the eggs are thrust by the female singly into the substance of the leaf on the lower side, either into the midribs and large veins or in the intervening spaces." Photo- graphs were taken of the eggs in the leaf in 1898 by Professor Wood- worth of this station, and these are still on file here. The first complete 1 *-•--, Iff $*&& ■\~f / i "S ' ' ■ . '*< 7 ! - . . 4 L Fig. 8. The egg of the grape leaf-hopper photo- graphed in its natural position within the tissues of the leaf. The circular spot at the top repre- sents the eye of the developing nymph within. Greatly enlarged. 1 Insects Injurious to Vegetation, Flint Ed. 2 Bulletin No. 3, N. M. Aj?r. Exp. Sta. 3 U. S. D. A. Yearbook, 1895, p. 402. p. 228. Bulletin 198. THE GRAPE LEAF-HOPPER. 187 account of the egg and the first published pictures were given by Slingerland 1 in 1901. It is now very well known that the eggs of this insect are laid just beneath the epidermis on the underside of the grape leaf. This is by far the most usual position, though they were occasionally found on the upper surface. They are generally distributed over the leaf surface, and occupy no special position in relation to the veins or ribs of the leaf. Some will be found in the tissue of the rib itself, a good many along the side of the ribs, and others scattered about over the general surface. They will be found also around the very edge of the leaf. In thousands of eggs seen during the summer we failed to find any arranged in rows as was found by Slingerland in New York. 2 ' The six or seven eggs laid in a row parallel with one another would represent a single laying of a hopper, and there is no reason why this should not be done occasionally, but it is not the usual occurrence here. We have found them with two or sometimes three arranged more or less parallel, but never more than this num- ber. In our individual breeding cages, where we obtained several hundred eggs, and where the space was limited, they were promis- cuously scattered about, one in a place. We confined several hoppers, taken in pairs, and liberated these in cages on currant, black- berry, loganberry and almond, peach, cherry, and a few other plants, but did not succeed in obtaining eggs from these food plants. In most cases the insects were found dead when the cages were examined three or four weeks later. We selected the particular plants named because they were convenient, and not because the eggs would be more likely to be laid on these than on other plants. Possibly more nearly related plants, botanically, would be found suitable for oviposition. The Virginia creeper is said to be readily attacked by this insect, 3 and we presume eggs are laid on this plant. Since, however, this species is a grape pest exclusively, that is, during the growing season, and all the experience indicates that it feeds only upon the grapevine, it may be stated, so far as the economics of the insect is concerned, that the eggs are laid only in the leaves of the grape. Fig. 9. The egg dis- sected from the leaf and photographed on a microscope slide. Particles of leaf tissue are shown still ad- hering to the egg. Greatly enlarged. 1 Cornell Agr. Exp. Sta. Bull. 215. 2 Slingerland, Bull. 215, Cornell Exp. Sta. 3 Gillette, Colo. Sta. Rept. 1900. 188 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Number. — The number of eggs which are laid by this insect, so far as we have been able to find, has not been previously recorded. It has been stated approximately as one hundred, and this, so far as our experiments went this year, is not very far from correct. We were able to make individual records of a number of hoppers, and found that the Fig. 10. Experimental vine used in the laboratory for obtaining data on the life-history of the hopper. Cages used for confining the insects are shown on the leaves. number laid varied from forty to one hundred and twenty-one. These were under laboratory conditions, but not very different from that of the vineyard. The hoppers were confined in cages attached to the grow- ing leaves, as indicated in figure 10. These cages were made by cutting a square or rectangular opening in a piece of cardboard, on the underside of which velvet was glued with pile side outward. This rested on the surface of the leaf and on Bulletin 198. THE GRAPE LEAF- HOPPER. 189 the opposite side; for the purpose of holding the leaf firmly against the cage, a piece of transparent gelatine was used, it being cut to cor- respond with the pasteboard on the opposite surface. These were held together on the leaf by means of ordinary paper clips. Strips of fairly thick paper were glued on the upper side of the pasteboard, leaving one edge free, under which an ordinary cover glass could be pushed. These cover glasses could be readily changed and kept clean, and the specimens could be easily examined, if necessary, with a com- pound miscroscope. Only forty eggs were laid by two or three hoppers, but these probably died prematurely. This number was laid in about two weeks, which is a shorter period than most hoppers evidently live. One laid ninety-six, two one hundred and ten, and one one hundred and twenty-one. Since our observations in the field indicate that most of the hoppers continue to lay eggs for one to two months, the number of eggs laid will probably average from seventy-five to one hundred and twenty-five. Rate of Egg Laying. — In the case of three or four hoppers we were able to follow pretty closely the rate at which the eggs were deposited, and the total length of the oviposition period. The following tabulation for one of these is given below. The totals are carried out for each date : Copulated June 23d. Cage 51. Rate of Oviposition. Date. Number of Eggs Laid. Date of Appearance of Nymphs. Hatched Number. June 30 July 2 July 3 July 6 July 7 July 9 July 16 July 17 July 19 July 22 July 23 July 24 July 25 July 26 July 27 July 31 August 1 August 2 August 4 August 7 August 9 August 12 August 16 August 17, hopper dead. 13 14 19 35 35 45 57 63 68 75 75 79 79 79 79 85 85 85 91 105 107 111 121 July 10. July 17. July 18. July 19. July 20. July 22. July 23. July 24. July 26_ July 27- 13 40 43 49 52 53 58 60 62 63* ♦Total laid to July 17th. No further hatching record was kept for short intervals. Incubation Period. — A large number of hoppers were liberated on our experimental vines at 9 a. m. May 29th, and removed at noon 2— Bul. 198 190 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. on May 30th. About twenty eggs were laid on the vines within this period and the time for hatching noted. About half of these eggs were enclosed in individual cages and an accurate record kept on the whole number. The first nymph hatched on June 17th and the last June 20th, thus requiring a period of from seventeen to twenty days for the hatching period. The above records were made on eggs laid by the hoppers which had remained over winter and on the dates given. There was a great difference however in the time required for hatching of the eggs from the spring brood. The observations were made during July and August and included records on two or three hundred eggs. The period required for hatching here was from eight to twelve days, all of the two or three hundred eggs coming within this limit. We can account for the difference only in the higher temperature of the later months or in the character of the eggs from the two broods. There was not much difference between the temperature in June and July in the Lodi section, hardly enough to account for all the difference in embry- onic development. It may be possible that the vigor of the adults and the increased development of the egg when laid will account for this difference over the spring brood. The time required for the eggs to mature in the ovaries was de- termined as from five to seven days. A number of pairs in coitu were liberated in the cages and the first eggs laid in five to seven days later. Percentage of Eggs that Hatch. — The table indicating rate of ovipo- sition on page above shows that of the first sixty-three eggs laid every one hatched. The hatching was less accurately kept for the remainder, but we are quite sure that every egg laid by this particular hopper brought forth a nymph. In the case of forty eggs laid by another hopper, all hatched. With the layings from most of the hoppers in our breeding cages a very high percentage of the eggs matured. This was not true of all, however. In one case a hopper laid a total of thirty-five eggs, scattered along over a period of three weeks, and only five out of the thirty-five hatched. In another case fourteen eggs were laid by an individual and none hatched. This experience in the laboratory of a very large percentage of mortality in some layings was also observed in the field. On one side of a particular vineyard where hoppers were exceedingly abundant in 1907, the worst infested field seen during the season, there was a very great mortality in the egg stage. On a single leaf taken from this particular area we have counted a total of seven hundred and forty-seven eggs that failed to mature. These could be very readily detected on the leaf by the dead epidermis covering them, which was dark brown to black in color. The leaf was thoroughly sprinkled with these black areas, and showed Bulletin 198. TH E GRAPE LEAF-HOPPER. 191 fairly well in a photograph, but not distinct enough to reproduce here. Upon examining these eggs that failed to hatch they appeared not to have started their course of development, or in other words, were infertile. The egg itself was generally found to be fresh and intact, the black color on the leaf being due in most cases entirely to the epidermis over the egg. This was in a vineyard where the hoppers appeared in innumerable numbers in the early spring, and the eggs laid were from hoppers that had remained over winter. The mortality in the egg stage reduced their numbers to a very appreciable extent. What was true of this one vineyard in 1907 was observed very generally in the vineyards around Lodi in 1908. We tried to account for this failure of the eggs to mature from a number of causes, but the matter is still unsatisfactorily settled. We first started on the supposition that something in the nature or make-up of the leaf, or a bacterial or fungous disease of the egg, might be responsible. The underside of the leaves of these vines were covered over more or less with pubescence or hairs. That this might have some effect in a mechanical way by holding moisture and thus fur- nishing the best conditions for producing disease was not borne out, since the same conditions were noted elsewhere with practically no mortality. The hoppers themselves seemed to be as healthy as those elsewhere, and a miscroscopical examination showed nothing unusual. That the eggs were infertile seems evident, but the exact cause in this particular area is not yet accounted for. Males were present in their normal numbers, and our experiments thus far indicate that they do not reproduce parthenogetically. The exact causes of such conditions as these will largely account for the sudden disappearance of the hoppers after having become very abundant. It is well known that hoppers, like many other insects, have their ups and downs as regards numbers. In 1897 the hoppers were so abundant about Fresno during the winter that the people appealed to the University for aid in combating them for the approach- ing season. An investigation was undertaken by Professor Woodworth and headquarters opened for a season 's campaign ; the hoppers appeared in great numbers in the spring, as was to be expected from their abundance in winter, but the majority failed to lay eggs and none appeared to be normally productive, and as a result there were scarcely enough of the new generation produced to furnish good material for the investigation. From what is known of the history of the pest in the State, this is an example of what occurs more or less periodically. Effect of Oviposition on the Leaf. — So far as we could see the puncturing of the leaf tissues for egg laying had no appreciable effect on the functions of the leaf. In many cases it was hard to tell where 192 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. an egg had been after hatching. In others the epidermis was blackened. In the case of the mortality in the eggs, already referred to, these spots were very numerous ^ and probably interfered somewhat with the normal functions of the leaf, but ordinarily these small punc- tures have no noticeable effect on the leaf. THE NYMPH. The young, immature hopper is called a nymph. It differs from the adult chiefly in the fact that the wings are not fully de- veloped. These are grad- ually acquired with each of the five successive molts until after the last stage, when the adult with fully formed wings appears. The stages may be easily recog- nized by the development of the wing pads. The relative size is indicated in the pho- tographs (Fig. 11), which were all taken under the same magnification. The Hatching Process. — Several young nymphs were observed in the process of emerging from the egg cov- ering, and it generally re- quired from ten to fifteen minutes for this process. After remaining quiet for a few minutes just outside the eggshell they would move about until they found a suitable place for insert- ing their beaks for food, where they would remain Bulletin 198. THE GRAPE LEAF-HOPPEK. 193 quiet for some time. For a few days before the eggs hatch there is a conspicuous dark spot at one end of the egg, which represents the eye of the developing nymph within. It is at this end that the egg covering is broken and the nymph makes its way out. First Stage. — The young nymph upon hatching from the egg is a very small semi-transparent whitish creature with conspicuous red eyes. The wing pads are invisible. The head and thorax appear large in proportion to the abdomen, and the insect walks in a more or less wabbling manner. The length of the period from hatching to the first molt is four days. Second Stage. — After the first molt the conspicuous red pigment in the eyes is partly lost, and the form of the body becomes more cylin- drical. Indications of yellow markings appear on the thorax, and the wing pads just begin to appear as lateral buds. The length of this stage is two days. Third Stage. — The markings of the thorax become a little more prominent, and the wing pads appear as buds extending posteriorly to the caudal margin of the first segment of the abdomen. The hind margin of the thorax is curved or arched, as a result of the wing pads projecting posteriorly at the sides. The length of this stage is three days. Fourth Stage. — There is not much change in the general appearance, except that the wing pads are now conspicuously larger and extend to the caudal border of the second abdominal segment. The length of this stage is four days. Fifth and Last Stage. — The wing pads now extend to the caudal border of the third, or to the middle of the fourth, abdominal segment. The length of this stage is five days. After the fifth molt the fully formed wings appear, extending to beyond the tip of the abdomen. Some of the life-history work carried on to determine the number and length of the nymphal stages is indicated in the following table : Cage No. 52 53 54 55 56 57 60a 62 63 Hatched between- 9 p. m. July 17 to 9 a. 4 p. m. July 17 to 9 a. 9 p. m. July 17 to 8 a. 4 p. m. July 17 to 9 a. 4 p. m. July 17 to 9 a. 4 p. m. July 17 to 9 a. 6 a. m. July 22 to 8 a. 7 p. m. July 18 to 8 a. 7 p. m. July 18 to 8 a. m. July 18 m. July 18 m. July 18 m. Julv 18 m. Julv 18 m. July 18 m. July 23 m. July 19 m. Julv 19 First Second Third Fourth Fifth Molt, Molt. Molt. Molt. Molt. 7-22 7-24 7-26 7-30 8-4 7-22 7-23 7-26 7-30 8-4 7-22 7-24 7-26 7-30 8-4 7-22 7-24 7-26 8-1 8-6 7-23 7-25 7-29 8-2 8-6 7-23 7-25 7-29 8-2 8-6 - 7-26 7-31 8-2 8-5 8-11 7-23 7 24 7-27 7-30 8-4 7-23 7-26 7-30 8-1 8-6 Adult St>ige, Total. 17 17 17 19 19 If* 19 16 18 194 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Cage No. Hatched between — First Molt. Second Molt. Third Molt. Fourth Molt. Fifth Molt. Adult Stage, Total. 64 65 66 66a 67 68 70 71 69 8 p. m. July 19 to 8 a. m. July 20 8 p. m. July 19 to 8 a. m. July 20 6 a. m. July 22 to 8 a. m. July 23 6 a. m. July 22 to 8 a. m. July 23 8 p. m. July 19 to 8 a. m. July 20 6 p. m. July 19 to 8 a. m. July 20 6 p. m. July 25 to 8 a. m. July 26 6 p. m. July 25 to 8 a. m. July 26 12 m. July 23 to 8 a. m. July*24 7-23 7-23 7-26 7-27 7-23 7-23 7-30 7-30 7-28 7-31 7-26 7-26 7-28 7-31 7-26 7-26 8-1 8-1 7-30 8-2 7-30 7-28 7-31 8-1 7-28 7-28 8-4 8-4 8-2 8-5 8-2 8-1 8-4 8-4 8-1 8-1 8-7 8-3 8-5 8-8 8-7 8-6 8-9 8-10 8-6 8-6 8-13 8-13 8-11 8-13 18 17 17 18 17 17 18 18 18 72 3 p. m. July 26 to 8 a. m. July 27 17 From the above table it will be seen that the shortest time required to go through the five nymphal stages is sixteen days, and the longest period nineteen days, the average being about eighteen days. Summarizing the duration of each of the stages as given above, it will be, disregarding fractional days, as follows: Stage. Wing Pads. Duration of Stage. First . Invisible __ _.__ __ __ 4 days 2 days 3 days 4 days 5 days Second _ As lateral buds_- _ _ __ _ __ Third Extending to caudal border first abdominal segment __ Extending to caudal border second abdominal segment- Extending to caudal border third abdominal segment-- Total - -_ Fourth Fifth 18 days The total length of the nymphal life of the grape leaf-hopper in New York, as worked out by Slingerland, 1 is from thirty to thirty-three days. This is a difference of about two weeks from that of the same species in California. Climatic conditions probably account for this difference, although so far as temperature is concerned, there is not much difference between the section about Lodi in June and July and that of New York in the same months. Molting. — As a preliminary step to the actual shedding of the skin, the nymph becomes quiet for a short period, then the old skin splits on the thorax and the nymph with its new covering makes its way out. The actual working out from the old skin required about ten minutes, and in a very short time thereafter it is able to move about as usual. Immediately after emerging from the old skin the insect is white in color and fairly transparent. The tracheal system can be followed very readily, especially in the younger nymphal stages, after emerging from its old integument. During the process of emerging the old skin seems to be held on to the leaf by the claws of the feet, and these often remain for some time attached to the leaf. The last nymphal skin, however, is much more firmly attached than the earlier 'Cornell Exp. Sta. Bull. No. 215, p. 92. Bulletin 198. THE GRAPE LEAF-HOPPER. 195 east skins, and later in the season these last skins will be about all that will be seen adhering to the leaf. The accompanying picture, Fig. 12 (and on the cover of this bulletin), photographed by Mr. W. B. Parker, shows one of these cast skins and the adult which emerged from it. Habits of Feeding. — The young nymph upon hatching from the egg soon finds a suitable place on the leaf for inserting its beak, and begins to feed on the plant juices. The majority of them remain during the earlier nymphal stages on the same leaf from which they originally emerged, but later there is more or less migration to other leaves on the vine; but probably a large number re- main throughout their nymphal life on the same leaf. Leaves which had contained large numbers of eggs, some of which were hatched and some not, were always seen to be well stocked with nymphs, while other leaves immediately adjoin- ing were free from both eggs and nymphs. Leaves which had already lost most of their green coloring mat- ter were seen to have nymphs in abundance, while fresh green leaves near by, offering a better food supply, were observed to be very free from hoppers. Of course, the nymphs can not leap or fly, and so can not make their way from one leaf to another on different shoots unless they happen to be touching, or else crawl down to the base of the shoot and up on the new one. Leaves on the same shoot were observed to have a great difference in the number of hoppers, always being most abundant on the older and paler colored leaves, where the most eggs were to be found. Transfer to Other Food Plants. — In order to determine whether nymphs would mature if transferred to other food plants than the Fig. 12. Adult grape leaf-hopper just emerged. 196 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. grape, we confined large numbers of nymphs in all stages on apple, almond, currant, blackberry, and peach, and in each case practically all completed their development in due course. Some of these were left on their food plants long enough to pair and lay eggs, but we were unable to find any evidence of eggs having been deposited. In another place it has been stated that adult females which were known to be fertilized failed to lay eggs on these same plants. It may be inferred then that nymphs will mature on other food plants, but it is at least unusual, if ever, that eggs will be laid elsewhere than on the grape. THE ADULT. Time of Reaching Maturity.- — The first adults from the spring brood at Lodi were observed on June 8, in 1907, and on June 12, 1908, this being about two months after they had begun to feed on the vine in the spring. By the last of June newly emerged adults were very common. At this time many were seen pairing, indicating that they were fully mature. Feeding Habits. — The habits of feeding of the adults are not very different from those of the nymphs except that they move about more. They will be found in greatest numbers on the leaves around the base of the vine and feeding with the nymphs. All through the season the hoppers, in whatever stage they may be, will be most abundant in the interior of the vine. This is probably for protection, since the food supply is not as good as that on the outside of the vine, for the older and less succulent leaves are around the base of the vine. So far as the food is concerned it would appear that the new Fig. 13. The leaves near the tip of the growing shoot would better adult grape r . leaf -hopper, satisfy them, as is the case with plant lice and some other enlarged J ' r d?ameters 1Ve °^ tne SUC ^i n g insects. Copulation and Oviposition. — Adults of the spring brood were seen pairing during the last of June, and most commonly about the middle of July. An occasional pair was seen during the first week in August, but after this none were seen throughout the rest of the season. Egg laying began with the spring brood during the last week in June in 1907 and the same time in 1908. The overwintering hoppers were also still depositing eggs, so that there appeared an overlapping of the two broods. Activity and Migrations. — While there was more or less moving about among the hoppers in the same vineyard, no migrations from one vineyard to another were observed until about the middle of July. At Bulletin 19S. THE GRAPE LEAF-HOPPER. 197 this time, and later, hoppers were seen in some cases flying about the farmhouses some little distance from any vines. They were seen at night, and when the weather was warm and calm. They appeared not to be going in any particular direction. Such migrations or activity were only very occasional, and so far as we could see the numbers in the vineyards were not changed. In the cases noted there was no particular reason for the migration on account of food. We believe that favorable weather conditions caused greater activity on the part of the insects, and that they are just as likely to go back into the same vineyard as to make a distinct migration in a definite direction for change of food or other reasons. Activity of the Sexes. — Both males and females seemed to be equally active as seen from the proportion of the sexes taken in> the air with a net when disturbed, and the fact that they were found in all situations in about equal numbers would seem to indicate that there is no difference as regards the activity of the sexes. Proportion of the Sexes. Date Number Ex- amined. Males. Females. Per cent Males. Per cent Females. May 20_ May 20_ May 22_ May 22_ May 22_ June 8- June 8_ Totals 200 200 100 308 167 140 215 1,330 59 75 65 150 89 75 85 598 141 125 35 158 78 65 130 732 29.5 37.5 65. 48.7 53.2 53.5 39.5 45 70.5 62.5 35. 51.3 4H.8 4H.5 60.5 55 Differences in Coloring Due to Age. — The hoppers in winter are distinctly redder in color, i. e., the markings are more pronounced than at any other season. The reddish color becomes more conspicuous as the winter season approaches, after they have left the vine and began to feed upon their winter food plants. In the spring after they have been feeding for a few weeks on the vine they become distinctly paler in color again. This less conspicuous marking is then maintained throughout the life of the insect surviving the winter. While they have become distinctly paler in color after feeding for two or three weeks on the vine in the spring, they are not so pale colored as the newly hatched hoppers, and the individuals of the two broods may be distinguished for a time after their emergence. The hoppers of the second brood that are on the vines in the fall take on the more con- spicuous coloring with the approach of the winter season, and this more pronounced marking remains until after they have fed for a few weeks on the vine in the following spring. 198 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. The Varieties of the Species Comes. — Altogether there are nine varieties of this species recognized in the United States. 1 All the specimens taken on the grape this year abont Lodi and Fresno, Cali- fornia, were the typical comes, and the variety color adensis. The difference between these two varieties is that coloradensis has a black spot on either side of the scutellum at the base, while in comes these Fig. 13. A vine enclosed by a cheese-cloth cage, open at the top, for studying migrations. spots are wanting. Comes largely predominates, as is indicated by the following table. The specimens were mounted on velvet between two miscroscope slides, and collected on the dates given : Proportion of the Varieties of the Grape Leaf-hopper. Date. Slide. Num- ber. Comes. Colora- densis. 1—29 1 2 3 4 5 6 150 155 145 155 136 96 134 135 129 142 122 80 16 II— 17 20 16 11—15 13 January — June __ __. 14 V— 25 16 Total 837 742 88.64 95 Percentage. -_ 11.35 i 1 Gillette, Proc. U. S. N. M., vol. 20, 1898, p. 709. Bulletin 198. THE GRAPE LEAF- HOPPER. . 199 Gillette, in the publication cited, states that coloradensis is a very distinctly marked variety and one that seems to be confined entirely to the West. This does not mean that it is limited to the Pacific coast states, for it occurs commonly in Colorado, and it is also found in Nebraska, Kansas, and New Mexico. Specimens of the California varieties were sent to Professor Gillette and he replied that they were the typical comes and coloradensis, the same as he would collect on the grape in Colorado. So far as we know, none of the other eight varieties of the species have been recorded from this State. The Common Name of the Insect. — The insect treated of in this bulletin is probably best known by the vineyardists of the State as the "thrips" or "vine thrips." This name, however, is improperly applied to this insect, since the term "thrips" rightly belongs to insects of a different group. The true thrips, if they have any wings at all, have delicate fringe wings, and are not so active as the leaf-hopper. The thrips are very small, slender bodied insects, ranging from yellowish to black in color, and will be most easily found in flower cups, where they feed upon the sap of the different parts of the flower as well as upon the leaves. There are several injurious species of thrips, but none do much damage, so far as observed, to the grape. One particular species has become a very important pest to fruit trees in the Santa Clara Valley. To avoid confusion, therefore, the term ' ' thrips ' ' should be applied to such an insect as this in the Santa Clara Valley and elsewhere. The common name of the insect discussed in this bulletin, as adopted by the Association of Economic Entomologists is the "grape leaf -hopper. " This is generally shortened in this State to simply "hopper" or "vine hopper," and this may be specific enough here, since, when we speak of "vine" alone there is no mistaking the kind of vine referred to; and it is generally understood that all hoppers feed on the leaf. However, the correct common name of the insect, as officially adopted, is the Grape leaf-hopper. Preference for Different Varieties of Vines. — In many vineyards infested with vine hoppers it will be noticed that certain varieties of vines will be much worse attacked than certain other varieties. It may be easy, in the case of a single vineyard, to express in definite terms the preference shown by the hoppers for particular varieties; but in another vineyard in the same neighborhood these conditions may be almost reversed, so that one is hardly warranted in making a general statement that will apply to all conditions and all situations. However, certain facts were observed which may indicate a choice 200 UNIVERSITY *OF CALIFORNIA — EXPERIMENT STATION. on the part of the hoppers for particular varieties of grapes. In the Lodi section the two chief varieties of grapes grown are the Tokay and the Zinfandel. Throughout all this section, so far as we observed, a distinct preference was shown for the Tokay over the Zinfandel. The Mission vines are also readily attacked by the hoppers in this section. In a particular vineyard, which contained these three varieties, the Mission and Tokay were worst infested, — the Mission a little worse than the Tokay, while the Zinfandel was distinctly the least infested. In a vineyard at Madera, which was under observation for some time, the vines which were most resistant or were less readily attacked by the hoppers were the Fehr-Yagos, Zinfandel, Alicante Bouchet, Petit Bouchet, and Mataro. Of these the Fehr-Yagos and Zinfandel showed the least injury. In this question of preference for varieties, of course the difference in the degree of susceptibility of the varieties to an equal attack of hoppers must be taken into consideration ; i. e., some varieties may be more weakened than others, although the hoppers may be present in equal numbers. The actual difference in the numbers of hoppers, however, may be very readily determined by jarring the vines and observing the numbers flying about them. The difference in numbers in most cases is so great that there is little difficulty in judg- ing this. The larger numbers of hoppers will always be found on the vines showing the most injury unless, of course, it is on those vines that are so badly injured that most of the food supply is gone and they are obliged to go elsewhere for food. DEVELOPMENT. Length of Life Cycles.— Hoppers hatching from eggs in midsummer or early fall remain over winter and attack the vine as soon as the foliage appears in the spring. Here they feed for a month, after which egg laying begins, and which may continue for two months longer. This will take it to midsummer again, so that the length of this life cycle is approximately one year. Large numbers of overwinter- ing hoppers were enclosed in cheese-cloth bags in the vineyard, and the hoppers were observed to begin dying off in June, and by the last of July practically all were dead. Hoppers hatching from eggs laid in May and June begin laying eggs upon reaching maturity five weeks later. Egg laying continues for a month or two longer, when they in turn begin to die off, thus making the length of this life cycle from three to four months. Number of Generations. — The number of generations of the insect as indicated above is two. Although these broods may overlap one another they are very distinct, and, at least in the Lodi section in 1907 Bulletin 198. the grape leap-hopper. 201 and 1908, there was no indication of a third brood. There were two well marked periods of breeding, and none were seen pairing excepting during these periods. For the overwintering hoppers this period was during the last week in April and the first two weeks in May. For the summer brood, or those hatching from eggs laid in May and follow- ing, the breeding period extended over the last week in June and the greater part of July, the maximum pairing occurring about July 10th. The breeding period of this brood is thus seen to be greater than that of the winter brood because of the prolonged hatching period of the preceding generation, while in the case of the overwintering hoppers they all reach maturity at about the same time and pairing takes place within two or three weeks. The best evidence of the number of broods is indicated in the well defined periods of breeding, but this fact is further strengthened by the appearance of the nymphs. A couple of weeks after the maximum breeding young nymphs appeared in great abundance, while the appearance of the young gradually diminished as the time from these dates increased. By September 1st very few young nymphs were seen, and all stages of nymphs were gradually disappearing and none at all were seen after October 15th. If there was even a partial third brood it would be expected that young nymphs would be found up to the time the leaves fell from the vine ; but this would not necessarily indi- cate a third brood, for it might be due to the prolonged development of the second brood. The absence of any pairing of individuals of the second brood during the late summer or fall, and the young nymphs ceasing to appear at the normal time after the breeding period of the preceding brood, indicate quite clearly that there are two generations of the insect in a year. Comparison of Development in Other Localities. — At Fresno, one hundred and thirty miles south of Lodi, where the temperature is con- siderably higher than at the latter place, the hoppers go through apparently the same development, although the different stages in the life cycles appear from a week to two weeks earlier than at Lodi. Continuous observation was not made on the hoppers in the vicinity of Fresno, but several trips were made to this section during the season and the life history checked with that of Lodi, except that it was a week or two earlier. In a visit to this territory on October 20th no nymphs were found in any stage, and this would seem to indicate that there are but two broods as at Lodi. 202 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. NATURAL CONTROL. Climatic. — The sudden decrease in numbers of insects without any known specific cause, a condition frequently observed, is often attributed to the general and more or less indiscriminate term "weather condi- tions." Grape leaf -hoppers, are known to occur in excessive numbers more or less periodically, and, for lack of definite information, we ascribe the cause to climatic conditions. Whether these conditions have a direct effect in reducing the numbers through exposure, or through sudden increase or decrease of temperature, or through humid- ity, or the indirect effect of these influences in inducing disease, in favoring the development of parasitic and predatory enemies, in reducing fecundity, or in unfavorably affecting the food supply, are points not easily determined. We have, however, apparently some evidence on the direct effect of unfavorable weather conditions in reducing the number of grape leaf -hoppers. During March, 1907, there were two or three weeks of almost continuous rain. At the end of this period the hoppers were found dead in large numbers in all the vineyards in the Lodi section. Between seven and eight hundred dead hoppers have been counted under a single bunch of alfilaria. In certain vineyards that Fig. 15. The larva of were flooded with two or three feet of water the commonesf predatory hoppers were nearly all destroyed. This latter, of enemy of the hopper course, is an unusual condition, but unfavorable in California. weather conditions of winter or early spring no doubt destroy large numbers of these insects. Parasitic. — The grape leaf-hopper appears to be particularly free from natural enemies, and this is especially true of parasitic enemies. In many hundreds of eggs, nymphs and adults examined and kept in breeding cages during the season we did not find a single specimen parasitized. Predatory. — Most of the natural enemies of the hopper come under this category of predatory or predaceous enemies, but even this list is not large. The most common of these observed during the season was one of the aphis lions or larvas of a lace-wing fly (Fig. 15). These were present in most of the vineyards, and were frequently seen feed- ing on the nymphs of the hoppers, but their number was not large enough to have any appreciable effect whatever in reducing the abund- ance of the grape leaf-hoppers. Ladybird beetles and their larvae were also seen to feed upon the nymphs, but they did not occur in Bulletin 198. TH E GRAPE LEAF-HOPPER. 203 large numbers. Certain spiders which make their webs at the crown of the vine seem to depend for food very largely on the adult hoppers that are caught in their webs. Ants were occasionally seen carrying away young nymphs in their jaws. The ants were not long in dis- covering our supply of nymphs in the laboratory, which was on the second story of a building, and soon established a regular line of march, where they could be seen carrying away nymphs to their nest in the ground below. A small red mite was occasionally found on the hoppers at Madera, but we do not know that the hoppers were actually killed by this parasite. Fungous. — It is said that a fungus belonging to the genus Epusa destroyed the hoppers in Connecticut in 1890. x We saw no evidence of fungous disease during the past two years. Neither was there any great mortality of hoppers observed, except in the egg stage mentioned in another place, and in this case it seemed to be due to the infertility of the eggs rather than an attack of fungous disease. Since, however, these insects occur in large numbers and are closely associated, once a fungous disease gets a foothold, large numbers are likely to be destroyed. MECHANICAL CONTROL. Blowers and Suction. — On account of the habit of the hoppers of flying about in the vicinity of the vine when disturbed, it was thought that there might be a possibility of drawing them into a machine by means of suction. A suction machine was designed and is said to have worked successfully in capturing the Rocky Mountain locust in 1874 and 1876 when the notable outbreaks of these insects occurred. This principle of suction is also used in sawmills for carrying away the sawdust. We started out on this problem by experimenting with a ventilating fan run by a gasoline engine. It was possible to draw in good sized pieces of paper and other objects heavier than small insects, but the distance through which the suction worked with sufficient force was too short to be of any practical use against the hoppers. In order that such a machine may work successfully it would be necessary to draw in the insects for a distance of at least three or four feet. This might be accomplished with a very much larger fan, but this would involve the use of heavy machinery that would be unwieldy for use in a vineyard, so that we abandoned the idea of control by suction as im- practicable. With suction the air is drawn in with about equal force in all directions from the end of the tube, so that there is not much force at 1 Thaxter, R., Conn. Sta. Rept., 1890. 204 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. any particular point ; but the air is blown out of the machine in a very definite column and with much force. With our experimental fan, objects that could be drawn in only when within a range of a few inches, could be blown out many feet. This induced us to try blowing the hoppers into a funnel-shaped receptacle. For this purpose a large blacksmith's rotary bellows was used, with a large galvanized iron funnel three or four feet in diameter for the receptacle. The black- smith's bellows did not produce an air current of sufficient diameter; for this to work successfully the diameter of the current of air should be at least three or four feet, and this again would require bulky machinery. The hoppers also held on very tenaciously to the opposite side of the leaves when the air current was turned on them, and thus it was impossible to get them all off the vine. While this method of fighting the hoppers gave more promise of working success- fully than the suction method, it would necessitate the use of rather expensive and cumbersome machinery that would not appeal to the practical vineyardist. Torches. — On account of the difficulty of killing adult hoppers with any spray while they are in the air, we tried the torch as a means of overcoming this difficulty. The torch, which was tried, consisted of burning the kerosene as it left an ordinary spray nozzle which would throw a very fine mist spray. This was tried during the dormant season on the hoppers as they would fly up from the vegetation growing in the vineyards. Even with this many hoppers would escape around the edges of the flame, and this, together with danger of scorching the vine when in foliage, led us to put this method in the negative list of remedies. Dry Powders. — It has been very positively maintained by certain growers that they could kill the nymphs of the vine hopper very successfully by the use of air-slaked lime. In order to determine this we made a number of experiments by keeping nymphs in all stages in a vial and thoroughly dusting them and filling the air in the vial with lime, but many did not appear to be inconvenienced by this treatment. This method was carried out on a practical scale by thor- oughly dusting a row of vines through a vineyard by means of the French vermorel machine used in applying sulfur for the Oidium (Fig. 16). The air-slaked lime had no effect whatever, so far as could be observed, on the number of nymphs. Pyrethrum was used with better success in the laboratory experiments where the hoppers were confined, but the results in the vineyard were not at all satisfactory in controlling the nymphs. The expense, more- over, of pyrethrum if used on such a large scale would be too great to make this a practical remedy. Bulletin J98. TH e GRAPE LEAF-HOPPER. 205 The idea that prevails with some, that sulfur is of use in killing the hoppers, is not borne out by facts. Hoppers, in all stages, confined in our breeding cages in the vineyard, thrived well in spite of the fact that large amounts of sulfur were blown into and held in the cages during the frequent sulfurings for Oidium. Sticky Shields. — Sticky shields have been used to some extent in fighting the grape leaf-hopper, but a large number escape by this Fig. 16. Applying air-slaked lime for the nymphs of the hopper by means of the French vermorel machine. method so that their use is not thoroughly satisfactory. A sticky shield held on .the leeward side of the vine and the hoppers jarred off will catch many, but a large number will not strike the shield. A three- sided box for our California vines works best, but even here many will drop to the ground or fly out on the open sides. In the New York vineyards, two men each carrying light sticky shields three or four feet high and seven or eight feet long on opposite sides of trellised vines, has been found to be a fairly successful method of capturing the hoppers. Probably the best sticky material for use on the shields in this State is the ordinary crude oil. 3— Bul. 198 206 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Fumigation. — A good many experiments were carried on with a view of determining the feasibility of fumigation as a means of con- trolling the vine hopper. The vines were enclosed either in canvas tents, or a galvanized iron tank or drum inverted over the vine, or a square box made of building paper (Fig. 17). In most of the experi- ments carried on the tank or box was used, since the air capacity did not vary in these as was the case with the loose canvas tents, and the dosage could be accurately calculated. One gram of cyanide of potassium to thirty cubic feet of space was "~ • — **■ """~ ^*djB|gAk