CHARACTERIZATION OF INSENSITIVE ACETYLCHOLINESTERASE IN INSECTICIDE-RESISTANT COTTON APHIDS, APHIS-GOSSYPII GLOVER (HOMOPTERA, APHIDIDAE)

Levels of insecticide resistance, total esterase activity, and acetylc holinesterase (AChE) sensitivity to inhibition by insecticides were in vestigated in three clones of Aphis gossypii Clover. Compared with LC( 50) values for a susceptible clone (171B), clone 968E showed high (> 2 0-fold) resistance to most of the carbamate and organophosphorus insec ticides tested, whereas clone 1081K only exhibited strong resistance t o some carbamate insecticides. 171B aphids had low esterase activity c ombined with an AChE variant showing baseline sensitivity to organopho sphorus and carbamate insecticides. 968E combined high esterase activi ty with broad-spectrum AChE insensitivity to these chemicals. 1081K ha d low esterase activity and an AChE variant that was insensitive to pi rimicarb and a smaller range of OP insecticides. These findings demons trate the occurrence of at least two insensitive AChE variants in A. g ossypii, whose contrasting insensitivity profiles permit rapid diagnos is using a kinetic microplate assay. Altered AChE appeared to be the m ain mechanism of resistance to both organophosphorus and carbamate ins ecticides in these clones. (C) 1996 Academic Press.