AMPLIFICATION OF A SERINE ESTERASE GENE IS INVOLVED IN INSECTICIDE RESISTANCE IN SRI-LANKAN CULEX TRITAENIORHYNCHUS

Culex tritaeniorhynchus, the major vector of Japanese encephalitis in Sri Lanka, is resistant to organophosphorus insecticides, with a 10-fo ld resistance ratio at the LC,, for chlorpyrifos, and a high heterogen eity factor in the insect field population. The major mechanism of res istance In this species, as in the mosquito C. quinquefasciatus, is el evation of esterase activity. Basic biochemical, immunological and mol ecular analysis suggests that the C. tritaeniorhynchus CtrEst beta 1 g ene is orthologous to the C. quinquefasciatus amplified Est beta s, Th e Est beta 2(1) antiserum cross-reacts strongly with CtrEst beta 1(1). Its corresponding cDNA, over the 545 base pairs sequenced, has simila r to 84% identity with the various C. quinquefasciatus Est beta s, The gene is amplified in C. tritaeniorhynchus. Amplification of the same esterase in two independent species, along with multiple amplification events involving this esterase gene in C. quinquefasciatus suggests t hat the location of this gene within the genome predisposes it to ampl ification.