3 * RY ANT BOARD March 1946 E-684 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine SUMMARY OF 1945 DDT INVESTIGATIONS FOR CONTROL OF FOREST INSECTS WITH SPECIAL REFERENCE TO AERIAL APPLICATION By F. C. Craighead and R. C. Brown Division of Forest Insect Investigations The promising results in the control of forest insects with DDT in the preliminary work of encouraged planning tests on a much larger scale for the 1945 season, primarily aerial applications. The high toxicity of DDT and the consequent effectiveness of low dosages, its ease of formulation in sprays, and the long residual effect give a combination of factors especially favorable to aerial application. Thus, for the first time, there is promise of developing practical and economical methods for the control of widespread infestations of certain forest insects, such as defoliators. Coincident with these developments, the extensive outbreak of the spruce budworm in Canada and the threat of its spread into our Northeastern States provided the stimulus for obtaining additional funds to study this problem in the United States. Results of the season's work are here briefly brought together for the purpose of analyzing the over-all picture. Many workers are mentioned who will later present detailed reports on special phases of the problem. The program, which involved a number of cooperators in the United States and Canada, had the following objectives: 1. The determination of the most effective spray formulas for aerial application of DDT and the mini mum dosages necessary for the control of the spruce budworm, the gypsy moth, and other forest insects. 2. The development of better equipment for airplanes for dis- tributing sprays over the forest and the working out of operational problems. 3. The determination of the biological effect of DDT on bene- ficial insects and wildlife in the forest. General Plan of Experiments and Cooperation The experimental work was conducted in cooperation with several other organizations. Without their whole-hearted active cooperation it would have been impossible to carry out more than a fraction of the program. The greater part of the work centered around the spruce budworm, because of the obvious threat to the timber in the North- eastern States, and around the gypsy moth control program. The spruce budworm work was tied in closely with that of the Canadian Division of Entomology, Forest Insect Investigations. Through J. J. de Gryse, in charge, the cooperation extended to the Department of L:-*nds and Forests of the Provinces of Ontario and Quebec. In Ontario the spray applications v.ere handled by R. N. Johnston, chief of the Division of Research, and in Quebec by L. Daviault, chief of the Bureau of Entomology, In the Northeastern States, V?. II. Foss, superintendent of Forest Pest Control, New York State Conservation Department; H. L. Bailey, director of the Vermont Division of Plant Pest Control; J. G. Conklin, of the University of New Hampshire; and R. E. Rendall and H. B. Peirson, of the Llaine For- est Service, actively cooperated in spruce budworm surveys and studies. All experimental work with the gypsy moth was conducted cooper- atively with the Division of Gypsy and Brown-Tail Moths Control of this Bureau. Several State organizations participated in the experi- mental spray applications, including the Pennsylvania Department of Agriculture, Bureau of Plant Industry, through T, L. Guyton; New York State Conservation Department, through W. LI. Foss; and the Connecti- cut Agricultural Experiment Station, through R. E. Friend. The development of spraying equipment for planes was handled through the Division of Agricultural Engineering of the Bureau of Plant Industry, Soils, and Agricultural Engineering, D. A. Isler having immediate responsibility for this activity. During the war the United States Coast Guard developed the use of the helicopter in sea rescue work and at the same time, in cooper- ation with the manufacturers, began adaptations for its postwar use. A cooperative arrangement was set up between the Bureau of Medicine of the Navy, the Coast Guard, and the Bureau of Entomology and Plant Quarantine to test the helicopter for distributing insecticidal sprays. The experimental work was conducted in Connecticut, New York, and New Jersey. Orchards, truck crops, forests, and mosquito-in- fested swamps were sprayed. Lt. Com. J. S. Yuiil, of the Bureau of Medicine of the Navy, represented that organization in the project and D. E. Parker represented this Bureau, The Coast Guard assigned Ensign David Gershowitz as pilot and Roy 7«agner as mechanic. Studies of the broader biological effects of DDT on the general insect population of the forest were conducted in this Bureau by the Division of Forest Insect Investigations in cooperation with the Division of Insect Identification. The responsibility for determin- - 3 - ing the effect of DDT on other wildlife was assumed by the Fish and Wildlife Service, United States Department of the Interior, most of the studies coming under the immediate jurisdiction of A. L. Nelson, assistant chief of the 'Division of Wildlife, and E. W. Surber, of the Division of Fishery Biology. R. J. Womelsdorf , representing the Pennsylvania State Board of Fish Commissioners, gave much assistance in the treatment of trout streams. J. LI. Corliss, of the Division of Gypsy and Brown-Tail Moths Control, assisted greatly in this study. Types of Aircraft Several types of planes and apparatus were used in these experi- mental aerial applications of DDT. A Navy N-3-N trainer fitted with a 50-gallon spray tank and a pump, which fed the spray liquid into a hollow tube fitted with noz- zles and supported under the lower wing, was used for many of the applications. This distributing apparatus, constructed by D. A. Isler, was a slight modification of earlier equipment designed by this Bureau. It proved to be a very simple and satisfactory device. A White Standard plane fitted with the so-called spinner-disk device, developed for applying heavy, concentrated suspensions, was used successfully in much of the gypsy moth work. An Interstate-Cadet plane owned by a commercial company was used in tests against the pine tip moth and the spruce budworm in Colorado and Nebraska. A 2-inch pipe leading from the supply tank in the plane opened into a venturi under one wing. Four CANSO amphibian planes, each fitted with two spray booms, were used by the Royal Canadian Air Force in spruce budworm spraying for the Province of Ontario near Lake Nipigon. A Waco plane on floats and equipped with a spinner disk was used for the spruce bud- worm work at Kabonga, Quebec, which was conducted cooperatively by the Dominion Government and the Province of Quebec. Two Waco land planes fitted with spinner brushes were used by a private company in the hemlock looper work in Oregon. The Coast Guard helicopter (Army IR-A.) was equipped with a spraying device consisting of a pump, a tank, and a nozzle bar. It put out a very fine mist, with droplets averaging under 100 microns in diameter. The helicopter was capable of flying very close to the tree tops, and the downward rotor blast carried the finjp particles thoroughly through the foliage. Excellent control was obtained of practically all the insects which are susceptible to DDT. ilore - u - uniform distribution of spray droplets and better control of the size of the droplets can be obtained with the helicopter than when the spray is subjected to the influence of the slipstream of faster air- planes. The small type used in these experiments has definite limi- tations as to pay load, capacity, and range of operation. Much more work is needed with helicopters, particularly the larger types now being developed. The matter of distributing equipment and the type of plane most suitable and economical for treatment of large forest areas needs extensive investigation. Will large land planes, capable of carrying 2 or 3 tons and operating 100 miles or more from a central base, be more economical than small planes that are based locally thus ne- cessitating the trucking of gas, oil, and insecticidal materials to the different points of operation? Such problems seem to be more the problems of engineers than of biologists and probably can best be answered by the industry. Aerial Application of DDT Toward the end of the 1944 season it became evident that a con- siderable portion of the DDT solution released from airplanes was not reaching the forest canopy. During 1945 some effort was made to de- termine the amount of DDT that was deposited in the forest. In some instances only one-tenth to one-half of the insecticide was found to be deposited on the experimental plots. Under ideal conditions, such as often existed for an hour or so in the early morning, and with the plane flying close to the tree tops, larger amounts were recovered. Meteorological factors are of predominant importance. Under forest conditions it is hazardous to fly below 50 feet, and some pilots show a tendency to keop up around 100 to 200 feet with smaller planes and even higher with larger types. The deposition of these sprays under favorable meteorological conditions seems to be governed largely by the droplet size. The size of the droplets varies from less than 50 to about 500 microns, depending on the character of the solution and the speed of the plane. It appears that a large portion of the drop- lets less than 50 microns in diameter, when released at 50 or more feet above the tree tops, tend to drift about in the air and never reach the foliage. They may eventually evaporate, leaving crystals that fall ineffectively through the foliage. Pilots, in applying oil spray, have reported that they frequently fly through an oil mist sometimes 1/2 mile or more from the point of release. This loss of material has resulted in a tremendous variation in the control of the same insect, at different times and with the same dosage. Sometimes good kill was obtained with 1/4 pound or less of DDT per acre. On other flights even 1 to 2 pounds per acre gave poor - 5 - control. The loss of this material in terms of increased cost is not too important, but if no loss occurred the same plane load could cover two to five times the area. Again, under favorable atmospheric conditions all the material may be deposited and cause unnecessary mortality to useful insects and wildlife. Studies of the effect of DDT on aquatic life have indicated some danger witt a dosage of 1 pound per acre. On occasions, with heavier dosages at least, the spray has drifted considerable distances from the treated area and killed numerous fish in ponds. Consequently the objective should be to use no more DDT than the lowest effective dosage. Efforts to analyze and correct this condition were prosecuted throughout the season. R. H. Nagel and S. F. Potts, of the Division of Forest Insect Investigations, Donald Whittam, of the Division of Gypsy and Brown-Tail Moths Control, as well as D. A. Isler, of the Bureau of Plant Industry, Soils, and Agricultural Engineering, gave considerable attention to this problem the latter part of the season, in tests at Beltsville, Maryland. R. H. Carter, of the Division of Insecticide Investigations, and R. F. Anderson, of the Division of Forest Insect Investigations, aided in the development of a method in which dyes were used for estimating DDT recovery. Kenneth Stewart and Kenneth Graham, entomologists in the Canadian Division of Ento- mology, aided throughout these studies. The United States Weather Bureau gave considerable assistance through R. N. Culnan and others, who set up a weather station on the Beltsville airfield. It was found that the use of more viscid and heavier liquids tended to form larger droplets than did alterations in outlets and nozzles used in these tests. The pattern of the DDT deposit across the swath showed a high peak, often 50 to 80 feet wide and much above the desired dosage, immediately under the planej with a rapid falling off for 100 to 200 feet on either side. Much valuable in- formation on the dissemination and distribution .of DDT sprays was obtained. Formulations and Dosages Several formulations containing DDT, including oil solutions, emulsions, and suspensions, were tested. These preparations were made up with several solvents and carriers that left either a crys- talline deposit of DDT or a deposit of a tacky or oily nature. Several emulsifiers were also tested. Most of the applications were of 10- to 12-percent solutions, at the rate of 1 pound of DDT per acre, with some as low as 1/8 pound per acre. The volume of spray per acre was also important and ranged from 1/2 to 5 gallons; about 1 gallon appeared ample for most conditions. This work was largely in the hands of R. H. Nagel, P. B. Dowden, and R. A. St. George, of - 6 - ther Division of Forest Insect Investigations, in close cooperation vdth R. C. Roark, H. L. Haller, D. F. Starr, and R. H.Carter, of the Division of Insecticide Investigations. In general all these formulas and dosages were so effective that no conclusions could be reached as to their relative value, iiore concentrated solutions (25 to 40 percent) and less gallonage per acre need further study. Oil solutions are easy to make but more objectionable to handle than emulsions and suspensions. The last two present less of a transportation problem for use in out-of-the-way places. Long re- sidual effect was obtained with both emulsions and solutions. The suspensions were not sufficiently tested in this respect, but appeared to lose their toxicity more quickly. Differences in tox- icity appeared to depend much more on the dosage of DDT than on the formulation. Tacky or smeary films killed more quickly than crystal line deposits. As the work progressed it became more and more evident that for many insects dosages well under 1 pound per acre are entirely effect ive provided they are efficiently applied. Loss of material, as discussed elsewhere, proved to be the most serious problem in regu- lating the dosage. For the present it is recommended that for large areas, especially where fish streams are involved, dosages be kept at around 1/2 pound per acre and should not exceed 1 pound. Advice from experienced entomologists and biologists should be sought be- fore large areas are treated. The Control of Injurious Insects Spruce budworm (Archips fumif erana Clem.). Because of the widespread outbreak of the spruce budworm in Canada and of no known activity of this insect in timberlands of the Northeastern States, the treatments for this species were planned for Ontario and Quebec. This program was primarily a cooperative one. Late in the winter of 1944-5 representatives of this Bureau, the Dominion Division of Ento mology, and the Departments of Lands and Forests of Ontario and Que- bec held several meetings to make plans for accomplishing as much as possible through combined effort. This Bureau, with a year's experi ence in the aerial application of DDT, assumed considerable responsi bility for the technical features of this project. Three operations were planned. The first was carried out early in the. season on a series of small plots in Algonquin National Park, Ontario, to determine the minimum dosage that could be used later in the season. The second operation was begun 2 to 3 weeks later on a - 7 - series of 25- and 50-acre plots, totaling about 2,000 acres, in the Kabonga section of Quebec, in cooperation with the Dominion Division of Entomology and the Quebec Department of Lands and Forests. The Bureau of Entomology of that Province provided the plane, materials, living quarters for the men, and much of the assistance in this operation. The Canadian International Paper Company also gave some assistance. The third operation was on a much larger area (about 100 square miles) in the vicinity of Lake Nipigon, Ontario, which was treated by the Royal Canadian Air Force for the Ontario Depart- ment of Lands and Forests. All three operations were greatly disrupted by the peculiar season. Insect activity started nearly a month earlier than normal owing to an unusually warm spring, but was followed by a cold period of several weeks which retarded insect development. A late frost, which killed balsam buds, made it very difficult to appraise the results of the treatment. The Kabonga plots were most productive of results^ they indicated that the spruce budworm could be controlled with dosages of 1/2 to. 5 pounds of DDT per acre in several different formulas and gallonages. The difficulty in controlling the appli- cation of spray appeared to be the biggest factor influencing the results of these treatments. The Nipigon area was treated at the rate of a little less than 1 pound per acre. The final results are not yet at hand, but the operational report indicated that the spray was very finely atom- ized and drifted considerably so that much of it may have been lost. Much valuable information was obtained, however, on operational problems of so large an undertaking. Later in the season spruce budworm infestations were discovered in the Adirondack area of New York, and immediately steps were taken to conduct spraying experiments in cooperation with the New York State Conservation Department. W. G. Howard and W. M. Foss, of that Department, gave considerable assistance in this work. Three AO- acre plots were treated with l/A, 1/2, and 1 pound of DDT per acre in 1 gallon of xylene and kerosene about 1 week before pupation of the budworms. All dosages gave good results. A few weeks later, just as the moths were appearing, a 200-acre tract was sprayed at the rate of 1 pound per acre in an effort to destroy the moths and prevent oviposition. The results of this treatment will not be available until next year. On the Roosevelt National Forest in Colorado 120 acres of Doug- las fir were sprayed at the rate of 1 pound of DDT in 1 gallon per acre and 30 acres at the rate of 2 pounds of DDT in 2 gallons per acre. Esso Heavy Aromatic Solvent, Velsicol AR-60, and xylene were - 8 - used as solvents, and fuel oil No. 1 as a carrier. The spraying was done on May 17 about the time the young larvae moved from their hibernation quarters into the needles. This work was under the technical direction of N. D. Wygant, of this Division. A subsequent cold period greatly curtailed the activity of the larvae and killed many of the Douglas fir buds. From 60 to 80 percent control was obtained. Incidentally, plots in this vicinity that were sprayed with ground sprayers in May and June 1944 showed very good control in 1945. Thus, one treatment may give control of two generations, the larvae present at the time of spraying and the adult moths that come to oviposit several weeks later. Present indications are that aerial applications of DDT as low as 1/4 pound per acre will effectively control the spruce budworm. Whether treatment of rather large blocks would prevent mortality of trees in treated stands is difficult to s ay, but it is believed that such a treatment properly timed would at least delay tree mor- tality for several years during which time the more valuable timber might be salvaged. Gypsy moth ( Porthetria dispar (L.)). Several large tracts of woodland infested with the gypsy moth were treated with DDT to de- termine effective dosages and formulas and to study operational problems. Thirty-four plots, covering more than 1100 acres, were treated. Sixteen 10-acre plots were located at TJendell, Mass., one 50-acre plot at Athol, Mass., two 25-acre plots at Saxtons River, Vt., eight 35- to 65-acre plots near Hope, K. Y., five 35- to 95- acre plots at Moosic, Pa., and two plots, one of 97 acres and the other of I93>at Spring Brook, Pa. P. B. Dowden represented this Division in conducting this work. It was planned to begin treating the gypsy moth areas a month or so ahead of foliage appearance or egg hatch, relying on the residual effect of DDT to kill the newly hatched larvae, and then to follow with applications immediately after hatching, in mid- development of larvae, and in the later instars. An unusually early spring anddalays in obtaining aerial equipment made it impossible to begin operations on schedule. Work was initiated on April 29 and continued until larvae were full-grown. The range in dosages was 1/8 to 3 pounds of DDT in 1/2" to 3 gallons of liquid per acre. Several formulas were used, including solutions, suspensions, and emulsions. Practically all treatments were effective except the l/8-pound dosage. Further work is needed with early applications of the lower dosages and to make accurate comparisons with differ- ent formulas of solutions, emulsions, and suspensions. Pine tip moths (Rhyacionia f rustrana bushnelli Busck and R. - 9 - neomexlcana(Dyar^, Late in April 637 acres of ponder os a pine plant- ation on the Nebraska National Forest were sprayed for the control of tip moths. This work was supervised by N. D. VJygant. The Forest Service supplied the materials and hired the plane. Velsicol AR-50, xylene, and Esso Heavy Aromatic Solvent were used dS solvents and No. 1 and No. 2 fuel oils as carriers. One plot was treated with an emulsion containing Triton X-100 (an aralkyl polyether alcohol) as the emulsifier. The applications ranged from approximately 1/2 to 3 1/2 pounds of DDT per acre and the reduction in infestation ranged from approximately 50 to 95 percent with the heavier dosages. Here again unseasonable weather played a large part in reducing the effectiveness of the sprays because of the long interval of retarded insect development. In general, the results were very favorable, and more extensive treatments are planned for the coming year. No satisfactory or economical method for the control of this insect had been found previously. Hemlock loo per (F.nppia fiscellaria (Guen.)). A total of 2200 acres were treated with DDT for the control of the hemlock looper in Clatsop County, Oreg. , under the direction of R. L. Fumiss. The private owners of the timberlands and the State Forestry Depart- ment paid for material and application. The applications were made between June 5 and July 15, beginning with the first hatching of the looper eggs. Six formulas were used in dosages from 1/5 to 1 pound of DDT per acre, including a proprietary emulsion. The total cost of these applications was about $2.30 per acre. During the same period 9300 acres were treated with a lead arsenate concentrate at the rate of 10 to 15 pounds per acre, at a cost of approximately $3*50 per acre. Very cool and wet v/eather continued throughout the month of June, retarding development and hampering operations. These condi- tions undoubtedly tremendously affected the results, but, although control varied considerably, the over-all result appeared to be reasonably satisfactory. Saratoga spittle bug (Aphrophora saratogensis (Fitch)). On July 13 and H several plots, totaling 478 acres, of pine plantations in Wisconsin were treated for the control of the Saratoga spittle bug under the direction of H. C. Secrest, of this Division. The sprays were applied just before the adults appeared. Kerosene and fuel oil solutions were used with Velsicol AR-50 as a solvent and applied at rates from 1/U to 5 pounds of DDT per acre. Some control was ob- tained with 1/2 and 1 pound, at 2 pounds 50 to 80 percent of the adult spittle bugs were killed, and 5 pounds in 3 gallons of liquid gave 100 percent control. Further work should be done to determine whether effective control can be obtained with smaller dosages. It - 10 - is possible that the reduction in flagging, which will not be fully- apparent until the spring of 1946, may indicate that the 1-pound dosage will give practical control. Red-headed pine sawfly (Neodi prion lecontei (Fitch)). A total of 252 acres of red pine plantations in Oneida Co., N. Y., were treated on July 4 and 5 for the control of the red-headed pine saw- fly, under the direction of J. V. Schaffner, Jr., of this Division. Of this total, LV6 acres were treated at the rate of 1/2 pound of DDT in 1 gallon of liquid per acre, kerosene being the solvent, and 106 acres were treated with 1 pound of DDT in 1 gallon of a xylene- kerosene mixture per acre. About 40 percent of the sawfly eggs had hatched at the time of treatment. Practically complete control was obtained with the 1-pound dosage, and only a few larvae survived the l/2-pound treatment. It is possible that the eggs from which these survivors came did not hatch until after the residual effect of the lower DDT dosage had worn off. This illustrates the importance of synchronizing DDT application with insect development. Further ex- periments in aerial spraying for the control of sawflies should be conducted. White pine weevil (Pissodes strobi (Peck)). Plans were made to spray white pine plantations in New York for the control of white pine weevil adults early last spring before eggs were deposited. The abnormally early spring and lack of aerial equipment frustrated these plans, and it was possible to treat only a few small plots with hand sprayers. The small-scale tests indicated that dosages as low as 1/2 pound of DDT per acre would kill adult weevils. Mr. Schaffner also directed this 7;ork. The weevils feed on the bark of pine twigs for a few weeks in the fall, before going into hibernation. Consequently three plots, totaling 220 acres, in Jefferson County, N. Y., were sprayed from an airplane on September 13 for the control of the freshly emerged adult weevils. Dosages of 1/2 and 1 pound of DDJ in 1 gallon of solution per acre were applied. Results of treatment cannot be measured until 194.6. A more thorough study of the possibilities of combating this important pest of white pine by aerial application of DDT is planned for next season. Helicopter Applications Sprays were applied with a helicopter on anal 1 plots (5 to 20 acres) for the control of cankerworms, the gypsy moth, a sawfly (Pi prion frutetorum (L.)) on red pine, the orange-striped oak worm (Anisota senatoria (A. & S.)), the European pine shoot moth (Rhya- cionia buollana (Schiff.)), the elm bark beetles ( Scolytus spp.), -li- the periodical cicada CMaflicicada septendecim (L.)), ancM>he pine bark aphid (Pineus strobi (Htg. )). Dosages ranged from as low as 1/8 pound of DDT per acre on one of the sawfly plots to as high as 8 pounds per acre in an elm bark beetle plot. The main objective of the work was to study the adaptability of the helicopter for treat- ment of various types of areas under different conditions. AH ob- servers were favorably impressed with the operation of this type of aircraft for treatment of plantations and small wooded areas. One distinct advantage, in comparison with a fixed-wing plane, was the ability of the helicopter to operate from almost any small open space near the area to be treated. A disadvantage was the small pay load of spray which could be carried. Twenty-five gallons of spray was the maximum load that could be carried with safety by the machine used in these tests. In general, good control of the defoliators was obtained. The treatment was ineffective against the periodical cicada and the European pine shoot moth at the strengths applied. Further study is needed before any report can be made on results of treatment for control of the elm bark beetles and the pine bark aphid. Effect of DDT Sprays on the General Insect Population Many insects are not injurious. In fact, relatively few species are serious pests. The importance of insects in furnishing the principal food supply for many mammals, birds, fishes, frogs, and other animals is not generally appreciated. Likewise, the effect in- sects have on each other, particularly the beneficial effects of pre- dacious and parasitic insects in holding in check their destructive hosts, cannot be ignored. When applied over large areas DDT has been found greatly to reduce the insect fauna for various lengths of time. Considerable effort was expended during the past season in measuring these effects and in determining whether sufficient control of ob- noxious species can be obtained without too much interference with the beneficial and desirable insect species. Three large areas, of approximately 100, 300, and 1,200 acres, near Scranton, Pa., were sprayed with 2, 1, and 1 to 5 pounds of DDT per acre, respectively. C. H. Hoffmann and H. H. Swift, of this Division, and H. K. Townes and R. I. Sailer, of the Division of Insect Identification, conducted these studies. The areas were studied intensively just before treatment and, except for the 300- acre area, for a long period afterwards. Sampling methods were de- veloped, and a thorough and comprehensive knowledge of the insect fauna of treated areas and check areas before and after treatment was obtained. Much valuable ecological information was obtained aside from the main objectives. All treatments produced immediate and pronounced effects on the insect population. Tremendous numbers - 12 - of insects were killed, and the insect fauna was greatly reduced for a time. Flies, caterpillars, parasites of caterpillars, and leaf- hoppers were most severely affected. Llany of the moths, aphids, scale insects, syrphid larvae, and coccinellid larvae were either less affected or not harmed. Leaf -feeding and leaf -resting species were severely affected, whereas forms inhabiting soil and leaf litter apparently suffered very little. The rate of reestablishment of the insect population was in proportion to the degree of treat- ment. On the areas treated with the 2-pound and 5-pound dosages effects lasted about 2 weeks and 2 months, respectively, with grad- ual reestablishment of a population similar to that found in the check areas. Aquatic life was, in general, much more seriously affected than arboreal or terrestrial forms. One-half pound of DDT per acre can destroy tremendous numbers of aquatic insects, crustaceans, and other formg . This depletion of food for fish might have some effect on the stocking of the streams. One area, through which a stream flowed, was treated at the rate of 1 pound per acre, but actually only about 1/4 of a pound per acre was deposited in the water. The stream was practically depleted of insect life, but relatively little direct harm was done to trout. The fish population was determined by E. W. Surber, and further study in the spring of 1946 should show whether or not starvation resulted from the reduction of food supply. Much more research work is necessary, but present information indi- cates that as little as 1/4 pound of DDT per acre actually going in- to the streams should be avoided if possible. Effect of DDT Spray on Fish and Wildlife The Bureau of Entomology and Plant Quarantine, realizing the possible danger that DDT applications over extensive forested areas might have on fish and wildlife, requested the assistance and coop- eration of specialists in this field to aid in obtaining facts. In the spring of 1944 a cooperative agreement was entered into with the Illinois Natural History Survey/ and late that fall their report in- dicated high toxicity of DDT to fish when applied at rates of 1 pound or more per acre. In the spring of 1945 & cooperative agreement was made with the Fish and Wildlife Service, after which a program of work was arranged for that season by A. L. Nelson, E. W. Surber, and C. H. Hoffmann. Three large areas, many ponds, and three streams were treated during the summer. The principal facts obtained from this study were briefly stated in a press release of the Fish and Wildlife Service dated August 22, 1945, and will be fully reported in a forthcoming publication of the Department of the Interior. In general, fish in - 13 - ponds and streams can be seriously affected at rates of 1/J+ to 1 pound of DDT per acre. However, these amounts on certain occasions produced little effect on fish Life. Much more information is necessary. Birds and mammals are affected less than fish, at least directly, by applications of DDT sufficient for the control of forest insects. In the 1200-acre study area in Pennsylvania several dead and affected birds were found and there was a significant reduction in the number of insectivorous birds left on the sprayed area 3 days after the application. It was several weeks before it was repopulated. This reduction was due in part to the death of the birds, but the exact proportion attributable to this cause was not determined. Some of the reduction was due to birds' leaving the area because of lack of food. Parts of this area appeared to receive much more than 5 pounds of DDT per acre because of the drift of the insecticide. There was a heavy population of cankerworms and leaf rollers on oak, and num- erous caterpillars on other trees at the Urne of spraying, and in- sectivorous birds were freely feeding on them. No effects on birds were reported in the 100- and 300-acre areas in Pennsylvania. It is reasonable to conclude, therefore, that dosages which are quite satisfactory for the control of forest insect pests — i.e., l/U to 1 pound per acre — will not disturb the bird or mammal populations to any appreciable extent. However, it is not yet fully understood how these birds were affected, and until more is learned about the use of DDT, caution is necessary in applying it on large acreages. Further Work As indicated throughout this report, practically every phase of the nork touched upon is still in a preliminary stage of development. In the light of the past season's results it appears that the most important angles for further investigation in the immediate future are as follows: (1) It is essential to obtain a more uniform coverage and less loss in the spray materials liberated from airplanes in order to economize on materials and to avoid injury to wildlife. The relation between the viscosity and density of the spray fluids, particle size, pattern of dispersal, height of flying, and the amount of DDT de- posited on the foliage should be determined. (2) More work is needed on the toxic effects of DDT to fish and other wildlife. More must be known about the action of this poison on aquatic and terrestrial forms — in particular, how it kills. For example, are fish and birds affected through eating insects coated with DDT? If so, proper timing of spray applications could be of much importance in avoiding injury. II UNIVERSITY OF FLORIDA - u - (3) Further work is needed on the toxicity to insects of vari- ous DDT formulations, particularly a comparison of oil solutions, emulsions, and suspensions, and on the possibility of applying them in greater concentrations and less gallonage than the 10- to 12- percent solution in 1 gallon per acre used in most of the applica- tions of last year. (4) There are many operational problems in the use of planes for applying insecticides over forested areas. The size of the plane in relation to economic distances of operation from the base, height of flying to give the greatest safety within limits of ob- taining effective control of the insects treated, and marking of areas to aid pilots in securing satisfactory coverage are all im- portant to the practical control of forest insects by this means. An extensive series of cooperative tests in aerial application of DDT for the control of forest insects such as the spruce budworm, gypsy moth, hemlock looper, pine tip moths, spittle bugs, pine saw- flies, and white pine weevil were conducted in 1945. These experi- ments were designed to give information on minimum dosages needed for effective control, to compare various DDT formulations, to im- prove equipment used in releasing sprays from aircraft, and to study the effects of DDT on other forms of animal life in treated areas. It has been determined that DDT in low dosages is a very effective insecticide for the control of many forest insects— probably 1/8 to l/U pound being sufficient for satisfactory control of many forms when the material is effectively applied. Much more work is needed with emulsions and suspensions in order to study their effectiveness as compared with that of oil solutions. The emulsions and suspensions have certain advantages, the principal one being the use of water as a diluent. Suspensions are apparently less injurious to aquatic life. They form larger droplets, and less material is lost in application. Spray applicators for airplanes and operational problems need much more study. Much better control of the material distributed from planes is necessary before we. can take full advantage of the low dosage requirements and residual effect of DDT and at the same time avoid danger to fish and wildlife. Good progress was made in determining the degree of danger of DDT to animal life inhabiting streams and forests and the broader effects of DDT on the beneficial insect population in these environ- ments. In general, the control of many forest insects with DDT seems assured with dosages of sufficiently low volume to cause no serious permanent injury to beneficial insects and other animal life. The interested and itfiolehearted cooperation of the numerous individuals concerned representing Federal and State agencies, pri- vate owners, and commercial companies was in the final analysis the chief factor in the success of the season's work. Summary