STATE i'-'^^' „^28 Onited States Departaent of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine EQUIPMENT FOR THE DISPERSAL OF DOT -INSECTICIDES BT MEANS OF AIRCRAFT 2/ By C. N. Busman, 0. M. Longooy, and E. S. Eensley^ Division of Insects Affecting Man and Animals The development of equipment for the dispersion of insecticides is a necessary function in connection with investigational work on now insectioidal materials, because in many cases the efficiency of a material is largely dependent on proper methods of application. The early work with DDT for the control of certain insects of medical importance, -wdiich was under way at the Orlando, Fia., labora- tory of the Bureau of Entomology and Plant Quarantine in 1942, required immediate consideration of ways and means to apply this insecticide. Biological tests had fully demonstrated the value of DDT as a mosquito larvicide, and the material was also foiind to be useful for adult mosquito control when applied under outdoor conditions. The quantity of DDT needed per vmit rate of application as a larvicide was shown to be Buoh lower than that required for arsenicals. The possibility that this might be true for the control of adults over large areas prompted investigations on airplane equipment for the dispersion of DDT insecticides, since aircraft provide methods of application not practical or feasible with other types of equipment. Investigations were started in July 1943 at the Orlando labora- tory to develop suitable equipment for the application of DDT insecticides for use by the armed forces. Since that time several types of equipment for the dispersal of sprays and aerosols by aircraft have been designed and tested, and this report discusses in detail some of the equipment developed. Other agencies have also carried out further studies on this problem, and mention is made of the equipment developed by them but tested in cooperation with the Orlando laboratory, DDT in dust form was first applied from airplsxies in August 1943, The physical properties of the insecticide at this time were such that a powder containing 10 percent or more of the material was not suitable for dusting purposes. Because of this condition, and because 1/ Interim Report No, 0-110. {MC Insect Control Committee Report No. 151), A report to the Committee on Medical Research on work done under a transfer of funds, recommended by this Committee, from the Office of Scientific Research and Development to the Bureau of Entomology and Plant Quarantine. - 2 - eprava hare certain advantages over dust, studies were "begun on the development of spray equipment. Since the most effective particle size of spray to use was not known when this work was started, the first eqtiipment was designed to produce a reasonably fine spray with a wide range of particle sizes. 2ven late in I9U5 the best particle-size range for the various uses had not been determined, although it was known that good results could be obtained with small as well as relatively large particles. PORTABLE SPRAY UNIT Ir'Series Army Airplanes A portable spray unit for use on the Ir-U (Army Oub), J3-65, and HS-l Havy Cub was developed in October 19U3. It was simple in design, with a venturi beneath the fuselage of the airplane. The venturi kept the spray from coming in contact with the fuselage. The first model was small suad contained a IJ-gallon spray tank. A gear pump (1/2 inch), operated by a 2-bladed, wind-driven propeller, delivered the spray material from the tank to the nozzles under a pressure of 60 pounds per square inch. Two splatter-plate nozzles, each with a 3/32-inch orifice, were mounted on the trailing lower edge of the venturi . The droplets produced by this equipment were rather large. However, the equipment was used to conduct certain preliminary biological tests on mosquito larvae and adults, and served as a model for the construction of a larger and more practical unit. The tank of the larger unit holds 25 gallons of spray material. The unit is const iructed so that it can be Installed and removed from an L-U, a J3"65. or *Ji Nl-1 Navy Cub airplane. To install this equip- ment no structural changes are necessary in any of the airplane- fuselage members, nor is the center of gravity of the airplane changed by its Installation. As in the original unit, a gear pump (l/2 inch), powered by a 2-bladed, wind-driven propeller, forces the spray material to the notsles. Six splatter-plate nozzles are attached to the spray boom near the outer and lower edge of the venturi. Sach nozzle Is provided with a No. 60 wire-gage size orifice, although orifices of several different sizes were tested. The geaur pump operates at a pressure of approximately 50 pounds per square inch and at an air speed of 70 miles per hour. The spregr material used in most of the tests with this equipment con- sisted of 80 parts of f\iel oil and 20 parts of lubricating oil. - 3 - The delivery rate was 2 3/4 gallons per minute, A view of this spray tinit is shown in figure 1. This sprayer was specifically designed for the L-4; however, with slight modifications it can be installed in an Aeronoa (L-3), a Taylororaft (L-E), and an L-5, V^en the sprayer was operated at a pressure of 40 pounds, and the splatter-plate nozzles were provided with No, 54 wire-gage size orifices, the droplets ranged in diameter from 10 to 461/ alcrons. In early tests this equipment was used with various DDT solutions against larvae and adult mosquitoes. The swath width roconmiended was 40 feet with the planes flying at a height of 15 to 35 feet and at a speed of 70 miles per hour. The dosage was 2 quarts of solution per acre, i/rtiioh was equivalent to 0.2 pound of DDT per acre when a 5 percent concentration of DDT was employed. Army PT-17 (Stearman) Airplane The spray \init designed for the PT-17 (Stearman) airplane was a modification of one designed for the L-4 series. Details of this equipment are shown in figures 2 and 3. The tank, with a capacity of 60 gallons, was designed to fit in the front- seat compartment after removal of the seat and front control stick. The venturi was also similar to that used on the L-4 series but considerably larger. It was held in place beneath the fuselage by clamping it to the lower longerons. A gear pump (l/2 inch) was mounted on a bracket attached to the landing-gear strut. A 4-b laded, 18-inch, wind-driven wooden propeller was mounted on the pump shaft to build up pressure in the lines. The spray boom, situated near the lower trailing edge of the venturi, consisted of 12 nozzles provided with No. 60 wire-gage size orifices. A brake assembly was designed for the gear pump, the control being moxjnted in the pilot* s compartment so that the plane could be flown to and from the area to be treated without unnecessary wear on the pump. This equipment was moxmted at the center of gravity of the air- plane, and its installation required no structural changes in any jpeirt of the airplane. With an operating pressxare of 120 pounds per square inch the delivery rate of the spray solution was 7 l/4 gallons per minute. Tests showed that 8Ln effective swath width of 80 feet was obtained when the airplane was flown into the wind at an altitude of 40 feet* - 1^- The droplets ranged from 3 to 201/ microns In diameter. The PT-17 spray eqvilpment was ixsed extensively in connection with research at the Orlemdo lahoratory. For these tests a special spray tank was hullt which contained three separate coapartments holding 20 gallons each. A valve system was designed and mounted in the pilot's compartment so that the fluid could "be sprayed from any one (or all three) of the tank compartments at will. Smoke equipment, which will he discussed later, was installed on the same plane. It was possible, therefore, to apply three separate spray solutions and to make three smoke applications in one fli^t, BEEAKICR-BAH SPRAYER Although the original portable spray units produced satisfac- tory results, there were a number of objections to the equipment and efforts were made to make improvements. It was desirable to decrease the wei2:ht and air resistance of the equipment, and to provide for more uniform distribution of the spray. The first opportunity to construct and use the breaker-bar sprayer was afforded v;hile one of the writers, C. N. Busman, was on assignment in the Pacific with Research Unit No. 2 of the U. S. Navy. The equipment was designed for the TBM or TBP ainslanes and proved successful against mosquitoes in tests conducted by the Navy. Similar equiDment for the smaller planes was then designed at the Orlando laboratory. L-U Series Airplanes The new portable spray unit for the "L-h series airplanes uses the same tank, pump, and wind-driven propeller that were constructed for the original model, and the venturi is replaced by two breaker- bar spray booms, one mounted Tinder each of the wing struts. Details of this equipment are given in plates 1, 2, and 3f aJid parts of the equipment are shown in figures U and 5. The two spray booms are clamped to the wing struts Just otitside the slip stream. Each boom is 3^ inches long and has 2U orifices of a No. 71 wire-gage diameter; however, the orifices can be made larger if desired. The space between the two booms is 8 feet 6 inches, making a total of I6 feet 6 inches from the tip of one boom to the tip of the other. The spray booms axe constructed of 3/8-inch (i.d. ) aircraft tubing;, the 2U orifices, equally spaced, being drilled horieontally along the tube. A Duralximin spray-breaker bar, 5/8 by 1/U inch, with - 5 - a 5° convex face, is mounted on the tubing with a sppce of 1/2 inch "between the tubing and the bsr. The bpr is held in -nlace by three 3/l6-inch bolts, which are threaded so that adjustments can be made between the breaker bar and the tubing. When a U-bladed propeller is used, the spray material is forced through the orifices at a pressure of 70 po\inds, and the spray particles are broken up by the spray material impinging against the bar. Further break-up results from air stream flowing over the edges of the bar. As the spray material disperses it is well distributed between the two bars a short distance beyond the rear of the plane. Since the spray is forced out over a total length of 8 feet, It becomes dispersed through air turbulence caused by movement of the plane. With this equipment the effective swath width is 80 feet, as compared with UO feet for the original equipment. In the tests with this equipment the spray materiad consisted of 80 parts of fuel oil and 20 parts of No. 30 lube oil plus dye. When k 1/8 gallons of solution was applied per minute, the dosage of spray was 1.7 quarts per acre when the plsme was flown at 60 m.p.h., as compared with I.U5 qxiarts per acre when the plane was flown at 70 m.p.h. When 5 3/5 gallons of solution was applied per minute, the dosage was 2.32 quarts per acre at 60 m.p.h. and 1.99 quarts per acre at 70 m.p.h. The breaker-bar sprayer has advantages over the original sprayer when used on an L-U airplane, and it is the type now recom- mended for military vise. It is lighter than the original sprayer, and the absence of the venturi reduces the air resistance. A wider swath, smaller droplets, and a more uniform distribution of the spray within the swath is also obtained. The droplet diameters range from 10 to U6I/ microns. The delivery rate and size of the droplets can be readily changed by having available several sets of tubing with different sizes and number of orifices, L-5 Series Airplanes The L-5 airplane was more readily available in combat areas than the L-U. It is also somewhat larger and will carry a heavier pay load. For this reason it was desirable to adapt the same type of sprayer for use in the L-5 as was designed for the L-U. This was done by the Army Air Forces Board, Army Air Forces Center, Orlando, Fla,, in cooperation with the Orlando laboratory. The equipment is essentially the same as that for. the L-k but is somewhat larger. The spray tank has a capacity of UO gallons. The spray is delivered at the rate of 10 gallons per minute, and at a dosage of 2 quarts per acre an effective swath width of 110 feet is obtained at a plane - 6- speed of 90 miles per hour. The hreaker-"bar spray hoom is con- structed of 3/U-inch tubing, 5 feet long. PT-17 (Stearman) and ir3H3 Airplanes PT-17 and 1I3H3 airplanes, which were used by the Anay for prluary trainers, are suitable for the application of sprays and are available as Government surplus property, A breaker-bar type of sprayer was designed for the PT-17 which was similar in principle to the equipment described for the L-U, The details of construction are given in plates H, 5, 6, and 6a to 6h, inclusive, and in figures 6 and 7. Figure 8 shows the application of a DDT spray with a PT-17 airplane equipped with the breaker-bar spray unit. The unit is considerably larger than the L-5 breaker-bar sprayer. The spray tank has a capacity of 60 gallons, and the two spray booms beneath the wings have a total length of 2U feet. Each spray boom can be provided with the number and size of orifices req\xired to give the delivery and approximate droplet spectrum desired. The unit described has a delivery rate of 10/ gallons per minute when the 3/U-inch gear pumps are powered with a U-bladed, wind-driven propeller on each wing. The spray booms used in the test model were provided with 100 No. 70 wire-gage slie orifices (50 in each boom), and the spray was forced throu^ the orifices at a pressure of 100 pounds per square inch. At a dosage of 2 quarts of solution per acre, an effective swath of 120 feet is obtained when the plane is flown at a speed of 90 m.p,h. The droplets pro- duced by this equipment range from 10 to U6l/ microns In diameter. TBM and TBP Airplanes The breaker-bar spray unit for TBM and TBP airplanes was first constructed for use in the Pacific. The equipment is designed for the application of DDT in fuel oil. It is constructed so that no structural changes in the -olane are necessary when the equipment is installed, and the plane can also be used for combat. All parts used in the construction were procured from Naval Aviation Supply in the theater of operations. Photographs of parts of the equipment are shown in figures 9 and 10* The bomb-bay atixiliary gas tank available for this aircraft is used for the insecticide spray tank. The only modification on the tank is the installation of four outlets to feed the four electric pumps. These outlets are mounted on the top end of the tank, with four standpipes extending to the bottom. All other fittings on the tank, such as transmitter, filler, and breathers, are standard installations. - 7 - Four electric auxilipry 'booster fuel pumps (IT, S. Navy Stock No. TFD 9500) (fig. 11) are mounted on a bracket which is the dupli- cate of the rear "bracket supporting the tank. Two pieces of 3/^ inch plywood are "bolted to each side of the brackets, to which the pumps are bolted. The brackets and pumps are mounted in the rear of the bomb-bay compartment, learing working space between the tank and the pumps. The pump capacity is approximately UOO gallons per hour. These pumps are adjusted for a pressure of 27 pounds per square inch, and produce a 25-pound operating preeeujre at the nozzle. Power is furnished to the pumpe by the 2U-T0lt electrical system of the plane. The wiring is brought to the ptunps from the junction box mounted on the rear ports ide of the bomb bay. The switch, which is mounted on the portside of the cockpit J\i8t in front of the throttle, is easily accessible to the pilot. Xach spray nozzle, located on the tip of each wing, is fed by two pumps connected by a T, and the spray material is delivered to the nozzle by a 1-inch (i.d.) alumisum tubing. A 1 1/4-inch hole is drilled in an inspection plate on the fuselage and rubber grommet is installed. The 1-inch a^iuminum tubing leads out from the T Joint through this inspection plate, Prom this point it extends up to the lower part of the wing and then out to the spray nozzles. The tube lies flush against the wing skin, and is held in place by clamps (U. S. Navy Stock Ho. CSCO 6^4-) that are bolted to the wing by screws (8-36). Two short sections of oil-resistant hose are installed in the line so that it may be uncoupled to allow the wings to fold. The spray nozzlfs and brackets are constructed of molybdenum steel, with gaskets between the brackets and the wing. These are held in place with 1-inch drilled head screws (8-36) and are safety wired. The bracket plate is constructed of l/l6-inch plate. Han^^ers for the spray boom ere constructed of l/2-inch (i.d.) 0,035-'inch v;all- thickness aircraft tubing welded to the plate and also to the clamps that hold the spray nozzle in place. Cross braces are welded in the hanger for additional strength. The spray nozzle is constructed of 1-inch (i.d.) 0.035-inch wall- thickness aircraft tubing. Nineteen No, 50 wire-gage size orifices, equally spaced, are drilled horizontally along the tube. A breaker-bar spray constructed of l/U- by 5/8-inch Duraltimin is mounted on the tubing. The bar is held in place by bolting it to the tubing with 8-36 drilled head screws, with spacers between the tube and the bar. The screws must "be satfety wired. The following is a brief description of a unit built by the Ba- nana River Naval Base, Banana River, Fla. , from plans furnished by - g - the Orlando laboratory. This tmit is a sli^t modification of the original type constructed in the Pacific. The "bomh-'bay auxiliary gas tank is used for the insecticide spray tank. The spray material is pumped "by four electric auxiliary "booster fuel puaips (U. S. Navy Stock No. TTD 9100). Each pump has a capacity of 700 gallons per hour and is adjusted to give an operating pressure of 25 pounds per square inch at the nozzle. The spray booms, one under each wing (see fig, 10), are con- structed of 1 1/U-inch (i.d.) 0.035-inch side-wall aircraft tubing. Each boom is 12 feet lon^ and provided with 38 orifices of a No. HS wire-ga^e size. The size of the orifices can be changed to suit particular needs. A bar constructed of l/U- by 1-inch Duralumin is attached to each of the booms with a clearance of 1 inch between the orifice outlets and the bar. The face of this bar is flat. The spray material is forced through the orifices in the tubing, and the spray particles are broken i:^ by the spray material impinging against the bar. Further break-up results from air stream flowing over the edges of the bar, TB? and TBM planes equipped with this sprayer usually fly at a speed of 115 knots (132 miles) per hour. The plane is flo%rn with 15^ of flaps under average conditions. At this speed a delivery of 2 quarts of solution per acre is obtained flying swath widths of 250 feet. Droplets ranging in diameter from 10 to 3^1/ microns were produced by this spray. A new device for the breaker-bar type of sprayer has been con- structed and is being tested. It consists of screen wire 5 laches wide mounted in a frame k inches to the rear of the breaker bar. The device runs the full length of the spray boom, and is held in place by brackets which are clamped to the spray boom. Several frames have been constructed of different size screens, ranging from l6 to UO mesh. The spray produced with this attachment has smaller particles and is more eqxially distributed, EXHAUST-GENERATED SPRATS AND THSBKAL AEROSOLS Because of zhe promising results obtained with DDT sprays, and because pyrethrum smokes had shown some promise against flies and mosquitoes in early tests made by the workers at the Agricultural Research Center at Beltsville, Md. , equipment was designed for testing DDT smokes applied from airplanes. The exhaust was utilised to produce the heat required to generate the BDT smoke. Various types of thermal equipment for generating smokes and aerosols have since been investl^iated by different agencies. The kinds of equip- ment developed and tested on varlo\is types of airplames are discussed - 9- brlefly in the following pages* Insecticldal Smoke-Spray Squipment L-U Series AlrplcmeB ,— >The first smoke-spray equipment was designed for the L-U series airplanes, employing the same spray tank, pump assemMy, and venturi used with the Husman-Longcoy spray device. Copper pipes, which were attached to the eodsaust pipes. Joined in a T beneath the fuselage. A single ^-Inch pipe then extended through and to the trailing edge of the venturi, utilizing the venturi as a support. It was originally believed that the venturi would aid in the dispersion of the smoke, but this was later proved Incorrect and the pipe alone was used. The copper pipes were covered wholly or partially with asbestos to retain the heat* The spray material was forced through a nozzle located inside of each exhaust pipe, just behind the esdiaost blaze from the engine, A stainless-steel exhaust pipe was later employed, because it was found that the copper pipe did not withstand the heat. Tigure 12 shows this equipment installed on a Cub airplane, A nujnber of field and semlfield tests were conducted with this apparatus in the fall of 19^3* The fuel oil solutions used in these tests contained from 5 to 20 percent of DDT. Cyclohexanone was used as an auxiliary solvent with the hl^er concentrations of DDT, In some of these tests good results were obtained against adult salt- marsh mosquitoes and Anopheles larvae, although in general results were unsatisfactory. The heat of the exhaust volatilized a portion - of the DDT solution, resnlting in a rather intense smoke. The equip- ment did not, however, cause complete conversion of the material into smoke, since some spray was produced. On the basis of studies condticted by workers of the National Defense Research Committee at Columbia University and the Bureau of Entomology and Plant Quaran- tine at Beltsvllle, and later confirmed at the Orlando laboratory, it has been concluded that the DDT smoke particles (less than 1 micron in diameter) are relatively nontoxic to insects. The mor- tality of larvae and adults obtained in some of the tests with the equipment described can, no doubt, be largely attributed to the spray particles. The eqtdpment described does not appear to be of practi- cal value* PT-17 (Stearman) Airplane , -'■Smoke^spray equipment similar to that on the L-4 series airplanes was installed by the Tennessee Valley Aathority (drawings used were furnished by Orlando labora- tory) on a PT-17 airplane (U50 hp,), and a similar device was designed for the PT-17 (220 hp,) at the Orlando laboratory. The equipment consisted of the same spray tank, pump assembly, valve, and spray line systems used with the original L-U spray unit, A 19-foot stain- - 10 - less-steel pipe, 5 Inches In diameter, made of two sections of equal length, and mounted along the side of the fuselage, was connected with the exhaust pipe of the airplane by means of a 2 3/^ inch (i.d. ) elbow and a piece of 2 3/l4-inch (i.d.) flexible tubing 8 inches long. The discharge end of the extension of the exhaust pipe was located beneath the tail of the plane. Tigure 13 shows this equipment on a PT-17 airplane, and figure lU shows an insectl- cidal smoke being dispersed from the same plane* The nozzles used inside the pipe were of various types of L- shaped jets, and were placed so that the spray was forced in the direction of the air stream within the pipe and the nozzles could be placed at different distances from the end of the exhaust pipe. When the nozzles were placed near the engine a high percentage of the DDT solution was of screening- smoke size (l micron or less), whereas when they were placed near the end of the exhaust-pipe extension a lar^e T>ortion of the solution did not volatilize but broke up into spray particles. Extensive experiments were conducted with this tyr^e of equip- ment by the Tennessee Vailey Authority. Excellent results were reported against Anopheles larvae and promising results against adults of Anopheles quadrrmaculatus Say. Some success was also obtained with this equipment in a few tests conducted at Orlando. As with the L-U smoke eq\iipment, however, the spray fraction was probably responsible for most of the toxic action. Thermal Aerosol-Spray Equipment The resTilts of tests with the insecticidal smoke-spray or thermal aerosol-spray equipment discussed in connection with the L-U and PT-I7 airplanes were of sufficient promise to warrant fur- ther study of the method for dispersing insecticides with exhaust- generated spray equipment. The National Defense Research Committee at the University of Illinois therefore designed equipment for the dispersion of DDT solutions as aerosols or fine sprays. Tests with this equipment were carried on in cooperation with the Tennessee Valley Authority, the U. S, Navy, the Army Air Forces, and the Bureau of Entomology and Plant Quarantine. The exhaust-generated spray equipment has been designed for several types of airplanes and brief mention will be made of each. PT-17 Airplane . — The first exhaust-generated spray unit for the PT-17 airplane was built by the Tennessee Valley Authority, These planes are powered by U50-hp, engines. The equipment consists of a venturi within the extension of the - 11 - e3chau«t pipe. The spray solution is injected through several small orifices placed at or near the constriction of the venturi. The rapid flow of the hot exhaust gases at the point of constriction of the venturi atomizes the solution into fine droplets. A portion of the solvent volatilizes and the insecticide is discharged as a screening smoke, altho\igh this is thought to represent only a small portion of the total material. Sxtensive e:q>erimental and practical control tests were con- ducted by the Tennessee Valley Authority in ISkh and 19^5, and satis- factory results have been reported against both larvae and adults of mosquitoes. Solutions containing as much sis 20 percent of DDT in Velsicol BE- 70 (chiefly tetramethylnaphthalene) were used in these tests* The sama type of equipment was also installed on a PT-17 aix^ plane from plans furnished by the National Defense Research Committee at the University of Illinois. In tests conducted against adult salt-marsh mosquitoes satisfactory results were obtained in only one test. These results were comparable with those obtained with spray apparatus tested at the same time. Details of the exhaust-generated aerosol equipment for the PT-17 airplane and its performance may be obtained from the National Defense Research Committee, Department of Physical Chemistry, Univer- sity of Illinois, Urbana, 111.; and from the Health and Safety Department, Tennessee Valley Authority, Wilson Dam, Ala* Navy TBti Airplane . — The same type of exhaust spray equipment as was used on the PT-17 airplane has been designed by the National Defense Research Committee at the University of Illinois and installed in a Navy TBM airplane. Tests conducted in Florida, Panama, and elsewhere indicated satisfactory biological results against Anopheles larvae and also against adults of A. albimanus Vied. , trianntjulatus Neiva and Pinto, and punctimacula "b. and K. The agencies cooperat- ing In these tests were the U. S. Navy, the National Defense Research Committee, the U. S. Army in Panama, the Tennessee Valley Authority, and the Bureau of Entomology and Plant Quarantine. C-U7 Airplane .— Rather extensive tests with the exhaust-generated aerosol equipment installed on a C-U7 transport plane have recently been conducted by the Army Air Forces Board, Army Air Forces Center, Orlando, in cooperation with the Orlando laboratory of this Bureau, and the National Defense Research Committee. Resxilts of these tests will be discTissed in a special report* - 12 - OCHXE TTFXS 0? SQmPICVT fOB TEB DISPSBSAI OT IBSXCTICIISS 7BXM AIRPLAnS Other tTpet of tpragr eqtdpnent have been imreetlgated by rarloot agencies, principally the Araj Air forces Board at Orlando. Soae of thete are in practical Tiae \3j the anted serricee at the present tiae, while others are in the experimental stage. The various types of equipnent known to hare heen tested will only he Mentioned here» and reference will he nade to known sources that nay he consulted for Bore detailed infonatlon* OheBical Warfare Service Tanks Soon after initial tests were nade which desionstrated that adult mosquitoes and larvae could be controlled with IDT sprays applied from small aircraft, preliminary tests were made by the Orlando laboratory t in cooperation with the Army Air forces Board at Orlando, to determine whether DDT sprays could be applied from the K-10 and M-33 tanks used by the Chemical Warfare Service. Fairly satisfactory results have been reported and, since ths equipment was already available in combat areas » it was serving a useful purpose because It could be employed in the absence of eqrxip- ment designed specifically for dispersion of Insecticides. The limitations on the use of the equipment were the rather low pay load and the lack of suitable methods of controlling the delivery of ths spray material. Since sufficiently good results were obtained with these tests, no further practical tests were conducted by the Army Air Forces Board at Orlando. This method of dispersing DDT sprays was then explored further by the Army and Havy and also by the British. Details of the equipment and its performance may be obtained throu^ the Office of the Air Surgeon, Army Air Forces, and from the Chemical Warfare Service, Washington, D. C. Gravity Tesd Spray Iquipment for Use on C-U7 and B-25 Airplanes One of the most promising types of spraying equipment for use on large airplanes is the gravity feed equipment designed by the Army Air Forces Board at Wright Field, Dayton, Ohio, and the lational Defense Research Committee at the Uhiversity of Illinois. This equipment, installed on a C-Uj or B-25 plane, gave excellent results in tests conducted in Florida and Panama by various cooperating agencies. -13- Setails of the equipment and its perforaance aaj al*o "be ol)tained from the Office of the Air Surgeon, krmy Air Torces, Yaehington, D. C» Spray Iqulpment for Use on Helieoptert Several types of spray equipment hare "been tested on a Sikor* Bkj B.-'k helicopter, including ordinary spray nozzles mounted on spray 'booms, exhaust generated smoke^sprayers , and the hreaker* tar type nozzles. This work vae done by the U. S, Coast Guard, the Bureau of Medicine and Surgery of the U. S. Havy, and the Orlando laboratory. Satisfactory spraying equipment has been dereloped, and preliminary tests indicate satisfactory biological results. The use of a helicopter for dispensing Insecticides is in the experi- mental stage, hoverer, and its place in this field has not yet been determined. Details regarding equipment for this type of helicopter may be obtained through the Bureau of Medicine and Surgery of the U. S. Havy, Vashington, S. C, UOSTISQ SQK7I7KEBT Although sprays hare a nomber of adTantages over dusts when applied from airplanes, Insectlddal dusts have been widely used for the control of mosquitoes as well as agricultural pests. Since ODT can also be applied In dust form for the control of anophellne larvae. It seems appropriate to mention dusting equipment. ?or use by the armed serrices DDT dusts have the following disadvantages: (l) The physical properties of DDT dusts are such that uniform dosages are difficult to apply; (2) the problem of obtaining satis- factory diluents for dusts in combat theaters is usiially more diffi- cult than for liquid insecticides; (3) mixing DDT dusts in the field is generally more difficult than mixing liquid preparations; (U) although effective against surface-feeding leurvae, such as the anophelines, DDT dusts are not highly effective against culicine larvae; and (3) DDT in dust form is less effective againet adult mosquitoes than it is in a spray. Dusting equipment was used in some of the early work done at the Orlando laboratory. A portable dxisting unit, which was designed by the Bureau of Sntomology and Plant Q;aarantine for use on a smell plane, such as the L-U series and similar airplanes, is described below. Plane for the unit are shown in plates 7 aad S. The equip- ment installed on a J3-65 is shown in figure 1^. The portable unit is designed so that it can be readily removed - lU- and installed on the airplane. Ho structural changes or altera- tions of any of the aircraft neabers are required to install the unit, and the airplane can be used for other purposes when the equipment is removed. The hopper has a capacity of 6 1/2 cubic feet. It is mounted in the rear-seat compartment and is equipped with a dost-eealed coyer and adjustable cabin ventilators to protect the pilot from dust while in flight. The various controls and valves are also shown in plates 7 a^^ S. As with the spray, the venturi attached beneath the fuselage (pi. 7 and fig. 13) prevents the dust from entering the plane and also aids in forcing the dust downward away from the fuselage. The dust agitator is powered by a wind-driven propeller. By means of the feed-control valve located beneath the agitator, the pilot can change the rate of delivery of the dust while in flight. The dust flow can be quickly cut on and off by means of butterfly valves aotuited in the two throats which extend from the hopper to the venturi. The equipment is designed for applying arsenical dusts, and is made so that the rate of delivery can be changed to put out dusts at the rate of 1 to 20 pounds per acre while flying a 50'-foot swath. Ho doubt many other types of dusting equipment have been designed, and further information may be obtained from the Health and Safety Department of the Tennessee Valley Authority. GroraHAL COHSIDERATIONS IN THE APPLICATIOH OP IHSECTICIDBS 7R0M AIRCRATT Detailed instructions cannot be given for the application of sprays by aircraft, as severed different types of planes will be used. The directions suggested here are general, and outline prin- ciples that should be followed in applying sprays with any type of slow-moving aircraft. In routine applications the plane is flown back and forth over the area to be treated (pi. 9)* The distance between successive flights, or swath width, will depend on the type of airplane used, the quantity of spray to be applied, the droplet size of the spray, the rate of spray delivery, and the velocity and direction of the wind. The most effective swath width must be deter- mined for each type of aircraft and equipment. To assist in calcu- lating the interval required between swath widths in relation to the dosage of insecticide, spray delivery, and speed of plane, a chart (pi. 10) has been prepared. Droplet Sise The optimum droplet size for use in aircraft spraying for - 15- mosqulto control has not "been determined. No doubt for iise against larvae It will he different from that required for adult mosquitoes. However, good results have been obtedned against both larvae and adults of mosquitoes with I3DT sprays producing particle sizes rang*> ing from 10-^^60 microns in diameter. Until more is known on this subject it seems well to employ this range of droplet sizes. By using nozzles with orifices of different sizes, the spray can be broken up into a wide range of droplet sizes, some of which will be in the so-called aerosol range (less than 25 microns) and others in the range of 3OO to UOO microns. This range of droplet size assures thorough and \inlform coverage under a wide range of conditions. The small droplets are carried by the air currents, thereby giving a more uniform distribution over a wider swath, and the large drop- lets generally fall downward beneath the path of flight of the plane. Swath Width The delivery rate of the solution should be set according to speed and desired swath width to obtain the amount needed per acre of a given concentration of spray. At present 2 to 3 q^iarts per acre of a 5-porcent solution or enmlsion is generally recommended. The flights to determine swath width should be made at altitudes of 35 *o 150 feet flying into or downwind. The original TBM, equipped with the breaker-bar unit, was flown at II5 knots, using I5 degrees of wing flaps, and at 2 quarts of solution per acre an effective swath of 150 feet was indicated. The newer model, which was de- signed by the Orlando laboratory and recently installed on this plane by the Banana River Naval Air Station, produces a wider, more effective swath at the same rate of application per acre. The breaker-bar type of spray unit installed on an L-H will give an effective swath of 80 feet, whereas 120 feet has proved satisfactory for the I1-5, both applying the insecticide at a rate of 2 qiMurts per acre. The PT-I7 can be flown at swath widths of 110 to 120 feet. The Tennessee 7alley Authority reports that the exhaust- generator tjTpe of equipment produces a wide swath. With the larger planes, such as the G-kf and B-25, equipped with grarity-feed spray equipment, an effective swath of 300 to 6OO feet is obtained. In apiolying sprays in open areas where there are no obstruc- tions, it may be desirable to fly light aircraft, such as the L-U series, at 35 ^eet or lower, the height depending upon the wind velocity. In a strong wind it is necessary to fly as low as safety permits to prevent excessive drift. With light planes sprays shotild not be applied when the wind exceeds 15 miles per hour. A breeze of about 5 miles per hour is an advantage in air applications, as the drift causes the spray from successive swaths to overlap and - 16 - insures more even and complete coverage. Under the same conditions, larger planes are flown at heights of 50 and 150 feet. The kind of spray, the natiire of the terrain, and the heists of the ohstractions usually determine the height of flight. This is particularly true of small planes. The recom- mended hei^t at which the C-U7 and B-25 should be flown (15O feet, as determined by the Arn^ Air 7orces Board) is usually high enou^ to clear obstructions. In areas with high obstructions it is sug- gested that small planes be flown as low as conditions of safety permit. An extra swath or two should be applied on the windward side, and ground obsenrers should direct the pilot so that these first swaths will fall just outside the area to be treated. If care is not taken, the drift may leave an untreated strip on the wind- ward side. When possible, sprays should be applied early in the morning. Wind conditions are usually most favorable at that time of day and there is less air tiirbulence. The importance of time of day has not been fully determined, but for the present early morning spray- ing is suggested as being most satisfactory. Pilots who have not applied duste or sprays should be trained before they axe assigned to airplane spraying. It is of primary importance that they be guided for the swath width tmtil they have demonstrated that they can fly even swaths without assistance. The degree of control obtained from airplane treatments depends very largely upon how uniformly the pilot maintains his flight or swath lines. In open areas a simple method of directing the pilot is to place flagmen at each end of the area to be treated; in wooded areata meteorological balloons may be \ised. Sach time the pilot flies over the markers the men move over the required number of feet to mark the next swath. Many pilots soon learn to judge this distance and do not require flagmen except in difficult terrain or in critical control situations. Where possible, a li^t two-way radio would be of advantage in directing the pilot, especially for spot spraying. A Uo-potmd transmitter and receiver is available for communication with the TBF or SB2C and other aircraft where the pay load permits. Plate 11 shows the flight pattern suggested by the Army Air Torces Board when C-U7 or B-25 aircraft are employed on small areas. Large aircraft are difficult to maneuver, and should be used only for large areas where the course is qtiite long. The large aircraft, such as TBM, B-25, SB2C, or O-U7, carry larger loads and thus redxxce the amount of time lost in the refilling operations. Also, their - 17- greater speed and flight range allow them to be used considerable distances from the base of operations. Small areas requiring short rune should be treated with small aircraft or by hand. The pilot is the key man in applications of insecticide from the air, although the over-all operation should be under the direc- tion of an entomologist. The success of the control operations depends on how well the pilot "flies" the area to be treated. He not only should be thoroiighly briefed on the problem, but he should work closely enough with those directing the control operations to be familiar with the problem. He should completely understand the object of the control program and its imT>ortance, He can better appreciate what is being attempted if he can be shown the problem on the gro\md. The difficulty of filling the spray tank on aircraft can be largely overcome by Uising a trailer tank equipped with a power pump. Such a piece of eqtxipment can be made easily by using a small air- cooled gasoline engine to operate a fuel puBip, This pump arrange- ment csm be mounted on a trailer tank having a capacity of 300 gallons or more. The hoses should be oil resistant and sufficiently long so that they can be used to fill the tank from barrels if nec- essary. The Chemical Warfare Service tank trucks have also been found useful for this purpose* t:) w 2; 1 a: jr^ H ^:^' c; o S '^0 T-1 :r^' hJ &H CO a u :3 o K hJ a; . CO <: JD f > l^ E^ t-< Pi. O W Oj „ |i! SiB (D o o c Ti .^ ^rr, bO ^;r K ^ (fl O 1 t, tn :r' m CL, hJ Q fj O ^N'^1''<^t0K^ «> STATE y^