Resistance in Anopheles culicifacies sibling species B and C to malathion in Andhra Pradesh and Gujarat States, India.

Studies conducted in Warangal, Khammam and Mahabubnagar districts in Andhra Pradesh and Surat district in Gujarat have revealed that Anopheles culicifacies sensu lato (s.l.) populations were resistant to malathion. In the absence of indoor spraying of malathion in public health programs in the 3 districts of Andhra Pradesh, resistance is attributed to the extensive use of pesticides in agriculture. Species B and C were sympatric in all areas surveyed, and both the species were resistant to malathion. In most of the surveys carried out in Mahabubnagar, Khammam and Warangal, levels of resistance were higher in species C than in B. In Mahabubnagar district an increase in resistance from 5.5 to 64% was observed from 1985 to 1987 in An. culicifacies s.l. The proportion of species C was low in the initial 2 surveys, and in the later surveys the proportion was almost equal to that of species B; the resistance level was also significantly higher than in species B. In Surat district, where resistance ranged from 74 to 93%, the level of resistance in the 2 species was almost the same.