INHIBITION OF ALTERED ACETYLCHOLINESTERASES FROM INSECTICIDE-RESISTANT COLORADO POTATO BEETLES (COLEOPTERA, CHRYSOMELIDAE)

Insecticide-resistant and susceptible strains of the Colorado potato b eetle, Leptinotarsa decemlineata (Say), were assayed to confirm the oc currence and define the specificities of altered acetylcholinesterases . Organophosphate and carbamate insecticides caused widely varying deg rees of inhibition, with no clear pattern of cross-resistance. In all strains, oxime carbamates were 5- to 10-fold less potent acetylcholine sterase inhibitors compared with arylcarbamates. One strain was relati vely insensitive to inhibition by eserine (4-fold). Acetylcholinestera ses exhibited the highest insensitivity to the insecticides used to se lect for resistance in each strain. Acetylcholinesterase from one stra in was insensitive to carbamates, and that from the other strain was i nsensitive to organophosphates. Inhibition curves were typically nonli near, indicating the presence of multiple acetylcholinesterase activit ies. Penetration studies showed no differences between strains in upta ke of carbofuran.