The effectiveness of ultra-low-volume applications of malathion at a rate of 6 US fluid ounces per acre in controlling Aedes aegypti in a large-scale test at Nakhon Sawan, Thailand.

The effectiveness of ultra-low-volume (ULV) applications of technical malathion to control Aedes aegypti was studied in Nakhon Sawan, Thailand, in November 1968. Two treatments of 6 US fl oz/acre (438 ml/ha) were applied 4 days apart by a C-47 aircraft equipped with a fuselage-mounted spraying boom. An area of 7 square miles (18 km(2)), which included the entire city area, was treated.The landing rate of adult A. aegypti adults was reduced significantly following each malathion application (95% and 99%, respectively), the reduction ranging from 88% to 99% during the 10-day post-treatment observation period. No eggs were deposited in ovitraps 4 days after the first application. Dissections of female mosquitos collected during the post-treatment period showed that only 8% of the females were parous compared with 30% before treatment and 40% in the check area. Night landing rates of other mosquitos were reduced by 82%-97%; housefly populations also decreased markedly. The test results indicate that UVL treatments with malathion applied by aircraft can be used to control A. aegypti during outbreaks of dengue haemorrhagic fever. The fuselage-mounted spraying system used in the tests performed very well. The equipment can be mounted on, and removed from, a C-47 aircraft very quickly, thus making it possible to convert such aircraft used for other purposes into spraying planes at quite short notice.