Responses of Anopheles minimus to DDT residual spraying in a cleared forested foothill area in central Thailand.

Anopheles balabacensis balabacensis and Anopheles minimus are the main malaria vectors in Thailand. In a cleared forested foothill area in the central part of the country A. minimus was the most prevalent anopheline species found, only 6 specimens of A. b. balabacensis being collected over a 3-year period. Cattle were scarce in the area, tractors being largely used for working in the fields. This situation contributed to high man-vector contact. A minimus occurred throughout the year, with a major peak of density in the dry cool season and a smaller peak in the wet season. The contact of A. minimus with man was much higher outdoors than indoors, and studies showed the species to be an early biter, especially in the dry season, thus increasing the chance of man-vector contact. DDT spraying appeared to reduce considerably the estimated vectorial capacities, however, this effect was not maintained and malaria transmission was not interrupted. Trials with supplementary or alternative attack measures are therefore indicated in this particular ecological situation.