POLYSUBSTRATE MONOOXYGENASES AND OTHER XENOBIOTIC-METABOLIZING ENZYMES IN SUSCEPTIBLE AND RESISTANT COLORADO POTATO BEETLE

The activities of key defensive enzymes against xenobiotics were studi ed in two azinphosmethyl-resistant and one susceptible strain of Color ado potato beetle (Lepinotarsa decemlineata Say) with emphasis on the microsomal polysubstrate monooxygenase system. Monooxygenase activity comparable to that in other coleopterans was observed in the oxidation of NADPH, O-demethylation of p-nitroanisole, N-demethylation,of amino pyrine, and epoxidation of aldrin. Aniline hydroxylase activity was no t detected. Monooxygenase activity against aminopyrine was largely con fined to the microsomal fraction of homogenates and was more active in the larval gut than in the fat body. Microsomal NADPH oxidation was i nhibited strongly in vitro by SKF 525-A and in vivo by prior treatment of insects with piperonyl butoxide. The activity of the monooxygenase system was approximately twice as high in the resistant strains as th at in the susceptible strain. Glutathione transferase activity was als o elevated in the resistant strains, but no elevation in carboxyestera se activity was seen. Piperonyl butoxide pretreatment increased the to xicity of azinphosmethyl several-fold more strongly in the resistant t han susceptible strain, indicating a significant role for monooxygenas e activity in resistance. However, in both strains, resistance to azin phosmethyl is multifactorial and enhanced monooxygenase activity is on ly one contributing factor. (C) 1994 Academic Press, Inc.