CHARACTERIZATION OF RESISTANCE TO ORGANOPHOSPHATE, CARBAMATE, AND PYRETHROID INSECTICIDES IN-FIELD POPULATIONS OF AEDES-AEGYPTI FROM VENEZUELA

Resistance to the organophosphates (OF) temephos, malathion, and pirim iphos methyl, and the carbamate propoxur was found to be low (<5-fold) in 3 Aedes aegypti populations collected from Falcon and Aragua state s of Venezuela. Resistance to chlorpyrifos (OP), permethrin, and lambd a-cyhalothrin (pyrethroids) was moderate (7-fold) in both populations. Mechanisms of resistance were investigated with the synergists pipero nyl butoxide (mixed function oxidase inhibitor) and S, S, S-tributyl p hosphorothioate (DEF an esterase inhibitor). Nonspecific esterase and oxidase enzymes played a significant role in OP and carbamate resistan ce, respectively. Resistance to pyrethroid insecticides was not affect ed by DEF or piperonyl butoxide. This suggested the presence of anothe r mechanism such as altered target site sensitivity (kdr). Biochemical tests showed significantly greater amounts of esterase activity in fi eld strains, whereas insensitive acetylcholinesterase was not involved in either OP or carbamate resistance. These results must be considere d in future control programs for Ae. aegypti, because OPs and pyrethro ids are currently used in vector control in most countries of Central and South America.