UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA CIRCULAR 282 February, 1925 Revised, June, 1930 PREVENTION OF INSECT ATTACK ON STORED GRAIN W. W. MACKIEi Seed grain is stored for a number of reasons by farmers and by cereal experimenters. Farmers commonly hold seed for a second year if it is clean and of high grade. Storing seed for more than one year kills certain fungi — for instance, ergot in rye and wheat. It is always advisable for farmers to hold a reserve of the seed of excep- tional or rare varieties which might otherwise be lost because of drought, hail, rain, insect pests, and destructive fungus diseases. The experimenter always finds it necessary to store seed for one or more years in order to maintain his stocks. All of this stored seed is subject to insect attack and most investigators have, at times, suffered irreparable losses in this way. The common method of combating insects in stored grain is by destroying them after they have begun to attack the grain and usually after considerable damage has been done. The three most reliable and commonly used insecticide agencies are (1) carbon disulfide gas, (2) cyanide gas, and (3) heat. Each is very effective when properly used with suitable equipment, but suitable equipment is often unpro- curable economically on farms and even in laboratories. Further disadvantages are the danger of explosions with carbon disulphide gas, asphyxiation by cyanide gas, and destruction or damage to seed germs if subjected too long to high temperatures and to carbon disulphide. In no case do these remedies prevent a recurrence of insect attacks. At intervals, more or less frequent, according to climatic conditions, a repetition of treatment is necessary. The cost of the chemicals and of the preparation of gas-tight containers or the special testing devices, is considerable. To this must be added the cost of labor. A remedy which would prevent all insect attack without the necessity of repeating the process and at a reasonable cost, would meet an urgent need. Such a remedy, under conditions Associate Agronomist in the Experiment Station. University of California — Experiment Station to be described, apparently has been found by accident in the treat- ment of wheat with copper carbonate dust as applied to prevent bunt or stinking smut. COPPER CARBONATE DUST AS A FUNGICIDE Before the experiments with copper carbonate as an insecticide are presented, it may be well, at this point, to describe briefly the use of this fungicide in controlling bunt. Within the last few years copper carbonate dust as a bunt preventive has come into general use on the Pacific Coast and in many other parts of the world where bunt is a serious limiting factor in wheat production. The virtues of copper carbonate dust as a bunt preventive may be enumerated as follows: (1) It equals the liquid fungicides bluestone and formaldehyde in destroying bunt spores, provided the seed is not visibly darkened with the spores. (2) It does not injure the seed — a contrast with the severe damage frequently caused by the two standard liquid fungicides. (3) Early and vigorous germination of the seed is fostered. (4) Seedling attacks by soil fungi, like Penicillium and Asper- gillus, are prevented and bunt infection from soil-borne spores is greatly reduced. (5) Better percentages of germination and better stands are secured than with seed treated by the liquid fungicides. It has been pointed out that the use of this fungicide results almost invariably in larger crops than those obtained when the seed is treated with the common liquid fungicides. Many farmers in several widely separated states therefore consider that copper carbonate dust applied to seed is very profitable even where no bunt is anticipated. The following experiments completed at the University Farm, Davis, California, will serve to illustrate the effects due to the copper- carbonate method of seed treatment. Three plots were drilled with bunted Hard Federation wheat treated as follows: table l Effect of Copper Carbonate; on Bunt 1 and Yiew> of Wheat at Davis, California Seed treatment Bunt, per cent Heads, 90 feet of drill row Heads, per cent compared with no treatment Bluestone — lime .44 6 65 .20 210 316 413 66.4 Check — no treatment 100.0 131.0 These results show an increase of yield, due to copper carbonate, of 31 per cent over no treatment and 65 per cent over the bluestone- lime treatment. Circ. 282] Prevention of Insect Attack on Stored Grain 3 As there are now a number of effective dusting machines for automatically treating seed as it comes from the cleaner and grader, the labor cost, a large item in the application of the liquid fungicides, is greatly reduced. Furthermore, a great advantage is secured by treatment of the seed in the slack season following the harvest, thus avoiding a loss of more valuable time at the important seeding period. This procedure is possible with copper-carbonate-dusted seed because of two effects of the chemical dust. First, copper carbonate does not in any way injure stored grain regardless of the length of time stored ; and, second, insect attacks are prevented. The latter condition will be shown in the experiments which follow. EXPERIMENTS WITH COPPER CARBONATE DUST AS AN INSECTICIDE Observations at Davis of wheat seed treated with copper carbonate dust, stored from a few months to two years, showed that no insect attacks occurred on dusted seed, while untreated seed in the same pile was literally reduced to bran by the attacks of the grain weevils, the confused flour beetle, and the Angoumois grain moth. Experiments in duplicate and at consecutive periods were conducted to determine the effect of the copper carbonate dust in preventing insect attack. A soft white wheat (Pacific Bluestem) was employed in these experi- ments because hard wheats are not so readily attacked by insects. The insects and seed were confined in stoppered bottles and the insects examined daily with the following results : TABLE 2 Effect of Copper Carbonate on Grain Weevils in Wheat Stored at Berkeley, California June 23 June 24 June 25 June 26 June 27 June 28 June 30 July 1 July 14 > i > T3 03 o> > o3 % 03 % "0 03 > 1 E 03 E 73 S3 a > 1 1-1 Q J Q hI Q *1 Q vA Q h-1 Q I-! Q ^ Q *i Q *Grain weevils; Wheat untreated.. 50 48 2 46 2 41 5 40 1 39 1 35 4 30 5 23 7 Wheat+CuCos, 2oz. per bushel.. 50 50 50 49 1 46 3 27 19 3 24 3 CuCo3 dust only.. . 50 49 1 48 1 36 12 19 17 7 12 7 tWheat+CuCos, 2 oz. per bushel. Cloth cover 50 50 50 35 15 25 10 18 7 7 %C on fused flour beetle Wheat +CuCo3, 2oz. per bushel.. 6 5 1 4 1 3 1 3 3 1 2 1 1 * Granary weevil (Sitophilus [Calandra] granaria (Linn.)) and rice weevil, S. oryzae (Linn.), t The cloth permitted about half of the weevils to enter the dusted seed but all died eventually on account no doubt, of breathing the dust. X Confused flour beetle (Tribolium con/usum Duv,). 4 University of California — Experiment Station From the very beginning, the weevils that came in contact with the copper carbonate dust showed distress and were very sluggish in their movements. The beetles, on the contrary, did not slow up in their movements. None of the insects apparently fed or laid eggs in the presence of copper carbonate. All of the weevils exposed to the dust were dead at the end of six days, and the beetles, at the end of eight days. Even those weevils which were prevented from coming in con- tact with the dusted wheat, but were exposed to the dust-contaminated air of the closed bottle, died as rapidly as those actually coming in visible contact with the dust. In another experiment, many hundreds of live Angoumois grain moths (Sitotroga cerealella Oliv.), confined in a jar half -filled with a portion of the same treated wheat, did not lay eggs although they lived for a period of three weeks or more, eventually dying of age without the production of larvae. THE NATURE OF CHEMICAL-DUST INJURY TO INSECTS Contact insecticides commonly are understood to be substances which, when dissolved or emulsified in liquid media, or contained in dusts, are capable of killing insects when brought in contact with them. In these experiments, we are not concerned with those sub- stances contained in the dust form which are stomach poisons and which therefore, to become effective, must be eaten. Dust contact insecticides cause death to insects, first, by fumes given off, second, by the entry of the dust particles into the respiratory system, and third, by corrosive action upon the softer portions of their bodies. The most important example of a dust insecticide of the first class is nicotine. It has been demonstrated that the walnut aphis is killed solely by the fumes from the nicotine dust. Certain entomologists believe, however, that particles of the tobacco dust pass into the trachea and are widely distributed to the tissues of the body, causing paralysis and death of the insect. This result appears to be confirmed by experiments with the melon and cabbage aphis, onion thrips, and cucumber beetles. Sulfur and lime have been used as contact poisons but have given either negative or poor results, Caustic lime may be effective against certain soft insects until it changes its form into air-slacked lime, or calcium carbonate. As the change from caustic to air-slacked lime is rapid the caustic effect is limited to a very short period. For this reason the application of lime to stored grain has not proved of much value against hard-shelled insects as the grain beetles and weevils. Circ. 282] Prevention of Insect Attack on Stored Grain THE ACTION OF COPPER CARBONATE ON INSECTS The injurious effect of copper carbonate dust on weevils appears first in their retarded movements. The insects become less and less active until death ensues. No weevil lives longer than six days after having come in thorough contact with this dust. The very evident distress of the insect in contact with the dust apparently causes a cessation of all feeding and reproductive activities. The beetles are naturally more active in their behavior and all die by the end of the eighth day of confinement in contact with the copper carbonate dust. Fig. 1. — Granary Weevil Sitophilus (Calandra) granarla (Linn.). Left, normal weevils. Right, weevils covered with the copper carbonate which killed them. The action of the copper carbonate is limited to its caustic effect. This chemical compound, consisting of varying proportions of copper carbonate and copper hydrate (CuCo 3 • Cu(OH) 2 ) is listed by chemists as insoluble in water but slowly soluble in certain dilute organic and inorganic acids. As the particles of copper carbonate dust are very adhesive even to extremely smooth surfaces, the rough-coated weevils and beetles soon become completely covered while crawling about in the dusted seed (fig. 1). The softer, moister surfaces, especially in creases between the joints of the legs, thorax, and prothorax, appear to be most affected by the chemical dust. No doubt a portion of the salt goes into solution through the action of the solvents on the moist, soft surfaces of the insects. This chemical reaction eventually causes death. 6 University of California — Experiment Station Undoubtedly minute particles of copper carbonate dust enter the respiratory system of the insects. In one of the experiments with weevils, the insects were screened away from the dusted seed con- tained in the bottom of the closed receptacle. These weevils, which did not come into direct contact with the copper-carbonate-dusted wheat seed, nevertheless died as soon as those which entered the mass of treated seed. This is readily explained when the amorphous, very finely divided condition of the copper carbonate" dust is considered. The dust is so light and impalpably fine that it remains suspended in air over long periods of time, and in a confined space is not carried away. Likewise, when copper carbonate dust is placed where wing- less, crawling insects, like the grain weevil, must come in contact with it in order to reach the stored grain, the seed is not attacked and, therefore, is fully protected against this class of insects. The Angoumois moth, which attacks all stored grain, even infests grain unharvested in the field. Wheat and barley stored in a pro- tected building, and not infested with beetles and weevils, were entirely destroyed by larvae of the moths at the end of the first year. At the beginning of the storage period a portion of the wheat and barley was treated with copper carbonate dust by the regular com- mercial treating machinery, at the prescribed rate of 2 ounces per bushel. After more than three years in the same storage with the grain which was destroyed by the moths, no evidence of injury to treated barley or wheat could be found in the treated grain. INSECTS WHICH SHOULD REACT TO COPPER CARBONATE DUST In the experiments described in this paper, the common grain weevils and beetles were effectively destroyed without injury to the wheat seed. Other insects in the weevil and beetle group likely to succumb to copper carbonate dust may include the rice weevil Sitophilus oryzae (L.), the saw-toothed grain weevil, Oryzaephilus surinamensis (L.), the foreign grain beetle, Cathartus advena (Walt.), the square-necked grain beetle, Laemophloeus pusillus (Schon.), the rust-red flour beetle, Tribolium femigineum (Fab.), and the small- eyed flour beetle, Palorus ratzeburgi (Wissm.). The benefits to be derived by the prevention of insect invasion of stored seed in the southern states or in warm regions by this simple and cheap remedy suggests trials in these areas. In conclusion, it appears from the results of these experiments that a new, cheap, very effective, easily applied remedy for the pre- vention and control of weevil and beetle attacks upon stored grain has been secured. Ciro. 282] Prevention of Insect Attack on Stored Grain MICE INJURY TO GRAIN PREVENTED Mice are a continual menace to seed grain stored on the farm and elsewhere. It is not usually possible to prevent them from get- ting into seed grain stored on the farm or in ordinary warehouses. The success obtained by copper carbonate in preventing insect attacks led to similar experiments directed at prevention of attacks on grain by mice. Mice, which do not require moisture other than that ordinarily contained in the grain kernels, were confined in cages and fed wheat treated with copper carbonate dust at the rates of 1, 2, and 4 ounces per bushel. The untreated wheat was consumed at the rate of 5 grams per day, or over 4 pounds per year for the adult mouse. Mice usually damage far more grain than they actually consume. A mouse eating 5 grams of treated seed per day would consume .0208 grams of copper carbonate, but a mouse leaves most of the chaff in eating grain and in so doing avoids consuming most of the copper carbonate held on the surface of the grain. Mice, when forced by starvation, consumed some copper carbonate with the wheat but did not show apparent injurious effects. When untreated grain or other food is available the mouse will not eat grain treated with copper carbonate. This dust acts as a repellent and affords full protection to stored grain. Seed grain should be cleaned and treated with copper carbonate soon after harvest to secure the benefits of full protection from insects and mice. HOW TO APPLY THE COPPER CARBONATE DUST Copper carbonate dust is applied to wheat at the rate of two ounces per bushel. Double this quantity is sometimes applied but is usually unnecessary and, besides, the fine dust is offensive to humans and to work animals. Machines are available for treating large quantities of seed grain in connection with warehouses. Portable machines driven by hand or by motor power are manufactured on the Pacific Coast. This latter class of dusters is adapted to farms of ordinary size or to groups of farms. For small lots of seed, a box turned upon an axle passing through the corners diagonally is fairly satisfactory. Copper carbonate may be also used to afford some protection to stored grain of any kind by placing it where crawling insects must pass it to get into the grain. It should not be placed on grain to be used for animal or human food. lOm-6,'30