Equipping a multi-engined aircraft with a fuselage-mounted spray system for the ultra-low-volume application of malathion.

J'/otes Equipping a Multi-engined Aircraft with a Fuselage-mounted Spray System for the Ultra-Low-Volume Application of Malathion * by CLIFFORD S. LOFGREN 1 HUGH R. FORD,2 ROBERT J. TONN 3 & SUJARTI JATANASEN 4 Early in 1968, a field trial was conducted with the ultra-low-volume (ULV) method of aerial application of insecticides in Bangkok, Thailand, for Aedes aegypti L. control (Kilpatrick et al., 1970). Two dosages of malathion ULV concentrate of 3 US fl oz/acre and 6 US fl oz/acre (approx. 219 ml/ha and 438 ml/ha) 5 were applied to 3 small villages on the outskirts of Bangkok using a Cessna-180 singleengined aircraft. The results of the tests with the higher dosage were very encouraging. Following 1 application the biting rate of A. aegypti fell from an average pretreatment count of about 15 per man per hour to 6 per man per hour. The biting rate dropped to less than 1 per man per hour following a second application 4 days after the first, then rose slightly after 2 days but fell again to a minimum of 0.37 bite per man per hour after a third application. The percentage of positive oviposition traps decreased from 50% to 0 during the same period. In the same area the Culexpipiensfatigans biting rate was reduced by about 90 %. A high kill of caged adult mosquitos placed within houses was achieved and 100% mortality of caged mosquitos placed outdoors occurred. The success of this field trial indicates that the judicious use of ULV malathion spraying may be useful in the interruption of an epidemic of haemorrhagic fever; however, if this is done over large urban areas, safety requirements would necessitate * From the WHO Aedes Research Unit, Bangkok, Thailand. This study was supported jointly by the Public Health Service Research Grant No. CC 00174 from the National Communicable Disease Center, Atlanta, Ga., USA, and by the World Health Organization. 1 Entomologist, Entomology Research Division, US Department of Agriculture, Gainsville, Fla., USA. "Agricultural research technician, Entomology Research Division, US Department of Agriculture, Gainsville, Fla., USA. 'Project Leader, WHO Aedes Research Unit, Bangkok, Thailand. ' Communicable Diseases (Control) Division, Ministry of Health, Bangkok, Thailand. ' Conversion factors: I US fl oz = 0.961 Imp. fl oz = 29.57 ml. 2462A the use of multi-engined aircraft. The swaths 500 ft (152 m) or more wide that are attainable with larger aircraft would greatly increase the efficiency and rapidity with which the affected area could be treated. It is very difficult in developing countries, however, to obtain suitable aircraft equipped with conventional insecticide spraying equipment. As a means of overcoming this problem, the World Health Organization decided to evaluate an existing insecticide spraying system 6 that can be mounted in the fuselage of C-47 aircraft and does not require wing-booms. This system and the rationale behind its development are described in a separate paper (Glancey et al., 1969). Essentially, it consists of a gear-pump, driven by a 12- or 24-volt motor, that pumps insecticide through a small boom mounted below the fuselage. Distribution of the insecticide is dependent on the production of small droplets that can be carried by cross-winds across the treatment area. The system can be installed or removed very quickly (<4 hours); thus an airplane can be converted for spraying and subsequently reconverted to its original usage very rapidly. On the basis of the preceding information a study was undertaken by the WHO Aedes Research Unit, Bangkok, to determine (1) the feasibility of controlling A. aegypti in a large city with ULV malathion applied at 6 US fl oz/acre (438 ml/ha) and (2) the suitability of the fuselage-mounted spray boom for ULV application of insecticides. This paper presents a description of the spraying equipment and the method of mounting it on the aircraft. The effectiveness of the system in spraying malathion for control of A. aegypti is described in a companion paper (Lofgren et al., 1970). Preparation and installation of spray rig The apparatus, as assembled for these tests, was mounted in a C-47 transport aircraft belonging to - 157 ' Designed by the Insects Infecting Man Laboratory, Entomology Research Division, Agricultural Research Service, US Department of Agriculture, Gainesville, Fla. - 11 158 NOTES the Royal Thai Air Force. Arrangements were made with the Royal Thai Air Force to install the spray rig and to make available the aircraft and a flight crew on test-dates specified in advance. Most of the parts for the spraying equipment were purchased in the USA; a few items, such as steel plates and plastic tubing, as well as materials for the barrelrack and welding services, were obtained in Bangkok. Installation of the system was carried out at the Royal Thai Air Force Base at Don Muang. Boom-assembly. The boom-assembly consisted of 3 sections of galvanized pipe fitted together in an inverted " T " formation with a bend in the middle (see Fig. 1). The lower section, which formed the actual spray boom, was 36 in (91.4 cm) long. It was formed by screwing 2 sections of pipe, 16 in (40.6 cm) long, into either side of a T-fitting and capping the open ends (Fig. 3). Positions for 10 nozzles were made by drilling and tapping holes, 3 in (7.6 cm) apart, along the boom. Nipples were placed in the holes and Tee-Jet nozzles were inserted. The upper vertical section of the boom-assembly was 48 in (1.22 m) long and this was joined, by a 450 elbow, to the middle section, which was 18 in (45.7 cm) long. The middle section was cut into 2 pieces and a union was inserted so that the lower boom section could be put on or taken off quickly. A flange of steel 1/4 in (6.4 mm) thick and 1 in (25.4 mm) wide was welded along the entire length of the upright section. Half-inch holes, 6 in (15 cm) apart, were drilled along the length of the flange, so that it could be fixed at different levels. The boom-assembly was installed in the following manner. A section of the floor over the inspection plates in the fuselage, near the cargo doors, was removed. The centre inspection plate in the fuselage was then removed. The upper section of the boomassembly, with the 450 elbow, was lowered through the hole with the flange towards the front and the section below the elbow pointing towards the rear of the plane. Two steel plates, 8 in by 18 in (20.3 cmx45.7 cm), with holes cut in the centre to fit the shape of the pipe and flange were placed on the pipe and positioned, one above and one below, the 2 airframe girders just above the inspection hole (see Fig. 1 and 2). The plates were bolted firmly in place with 6 bolts so that they formed a solid support for the boom. The upper plate had 2 small brackets welded to it, one on either side of the flange on the pipe. Holes in these brackets matched holes in the pipe-flange so that the entire boom assembly could be attached firmly to the plate with a short bolt. When (...truncated)