A prospective study of the effects of ultralow volume (ULV) aerial application of malathion on epidemic Plasmodium falciparum malaria. II. Entomologic and operational aspects.

In a large-scale study in the Miragoane Valley of Haiti, designed to test the effects of aerial ultralow volume (ULV) malathion on epidemic Plasmodium falciparum malaria, spray operations resulted in an immediate and sharp decline in numbers of the vector, Anopheles albimanus. The adult population of this mosquito remained at less than 1% of previous levels until several weeks after a 50-day spray period (27 October-16 December 1972) during which six cycles were completed. The study area offered ideal conditions of wind, temperature, humidity, and mountain barriers. Mosquitoes in the area were highly susceptible to malathion. Results indicated that aerial ULV treatment with malathion can reduce A. albimanus populations rapidly and effectively when applications are made over an area as large as 20,000 acres. Preliminary results showed that effective control was not achieved in areas one-quarter that size; these areas were not sufficiently large, and infiltration of mosquitoes from adjacent untreated areas was possible.

A re-examination of the disk flow regulator.

It is important in residual spraying programmes for malaria eradication that a uniform deposit of insecticide should be applied to the walls of dwellings. The uniformity of application with hand compression sprayers is greatly enhanced if a disk flow regulator is used, but this device has not been popular for field use as its properties alter after a few days' use. This study explains the mode of action of the device and discloses that swelling of the disk caused by the DDT formulation is the primary cause of the gradual reduction of output. The need for proper mating of the disk with the nozzle tip is explained, and the 9504E-type tip is described as best suited for the desired spray output. Use of the disk flow regulator is recommended because it permits uniform spray application and reduces nozzle-tip erosion.

Preliminary studies on the use of ultra-low-volume applications of malathion for control of Aedes simpsoni.

In view of the threat of additional yellow fever epidemics in East Africa and recent successes in the use of malathion applied by the ultra-low-volume technique against insect vectors, field trials were initiated in November 1968 to test the efficacy of this method against Aedes simpsoni. Results of these trials show that in areas where Musa ensetta is the principal breeding site, the application of 20.2 US fl oz/acre (1474 ml/ha) of malathion was capable of reducing vector populations 93%-100%. Comparable applications of 6 US fl oz/acre (438 ml/ha) reduced populations by 76% and 89%. Since this study did not conclusively demonstrate that the 6 US fl oz/acre dosage rate was sufficient to obtain maximum population reduction, further studies should be initiated to obtain information on the optimal dosage to be employed against this species.Under the conditions of these trials, the use of a light, single-engined aircraft equipped with a rotary atomizer spray system and capable of operation from improvised fields was shown to be feasible against this vector species. It was further demonstrated that the canopy formed by M. ensetta does not present an impossible barrier to the penetration of the spray droplets produced by the ULV application technique.Observations made on the application methodology and on the biology of A. simpsoni show the versatility of this species and the need for further studies on the integration of spray applications with the peak activity periods of the insect.