Behavioral responses of malaria vectors, Anopheles minimus complex, to three classes of agrochemicals in Thailand.

Behavioral responses of two wild-caught populations of Anopheles minimus complex, species A and C, exposed to operational field doses of three commonly used agricultural insecticides, carbaryl (carbamate), malathion (organophosphate) and cypermethrin (pyrethroid), were characterized using an excito-repellency test system. Test populations were collected from different localities in Kanchanaburi Province, western Thailand. Both populations showed strong irritancy by quickly escaping test chambers after direct contact with individual surfaces treated with each insecticide compared with match-paired untreated controls. Noncontact repellency response to cypermethrin and carbaryl was significantly pronounced in both A and C populations, but comparatively weak when exposed to malathion. Noncontact repellency produced much weaker escape response in both populations, but in some species-chemical combinations, it remained significant compared with controls. We conclude that contact irritancy is a major behavioral response of both A and C when exposed directly to any of the three compounds, whereas only cypermethrin produced a significant repellency response in species A.