Moores_1996_Pestic.Biochem.Physiol_56_102

Levels of insecticide resistance, total esterase activity, and acetylcholinesterase (AChE) sensitivity to inhibition by insecticides were investigated in three clones of Aphis gossypii Glover. Compared with LC50 values for a susceptible clone (171B), clone 968E showed high (>20-fold) resistance to most of the carbamate and organophosphorus insecticides tested, whereas clone 1081K only exhibited strong resistance to some carbamate insecticides.171B aphids had low esterase activity combined with an AChE variant showing baseline sensitivity to organophosphorus and carbamate insecticides. 968E combined high esterase activity with broad-spectrum AChE insensitivity to these chemicals. 1081K had low esterase activity and an AChE variant that was insensitive to pirimicarb and a smaller range of OP insecticides. These findings demonstrate the occurrence of at least two insensitive AChE variants in A. gossypii,whose contrasting insensitivity profiles permit rapid diagnosis using a kinetic microplate assay. Altered AChE appeared to be the main mechanism of resistance to both organophosphorus and carbamate insecticides in these clones.