Biochemical mechanisms of malathion resistance in Indian Anopheles culicifacies (Diptera : Culicidae) sibling species A, B, and C: Microplate assays and synergistic studies

Anopheles culicifacies Giles is a complex of 4 sibling species, A, B, C, an d D. In view of the differences among sympatric sibling species in the leve ls of susceptibility to malathion, a study was carried out to determine the resistance mechanism(s). The study was carried out in Andhra Pradesh and G ujarat states where species B and C are sympatric and in Uttar Pradesh and Haryana states where species A and B are sympatric. Microplate biochemical assays on field-collected malathion-resistant species A, B, and C indicated the noninvolvement of elevated levels of nonspecific esterases and insensi tive acetylcholinesterase. Bioassays with the synergist triphenyl phosphate (a specific carboxylesterase inhibitor) have indicated the involvement of carboxylesterase as the major mechanism of malathion resistance in these sp ecies.