Detoxifying Enzymes of Selected Insect Species with Chewing and Sucking Habits

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Abstract
Levels of glutathione S-transferase, carboxylesterase, and microsomal monooxygenases in two species of Lepidoptera (Plutella xylostella L. and Ostrinia furnacalis Guenée) and five species of Homoptera (Nilaparvata lugens Stal, Laodelphax striatellus Fallén, Nephotettix cincticeps Uhler, Hyadaphis erysimi (Kaltenbach), and Myzus persicae (Sulzer) were determined. For all species, activity of glutathione S-transferase was higher when 1-chloro-2,4-dinitrobenzene was used as the substrate than when 1,2-dichloro-4-nitrobenzene was used. Nilaparvata lugens, L. striatellus, and Nephotettix cincticeps had 10 to 30 times more carboxylesterase activity toward both 1-naphthyl acetate and 2-naphthyl acetate than the two aphids, H. erysimi and M. persicae, and the two lepidopterans. More microsomal monooxygenase activity (50–100 times) toward several substrates was detected in larvae of the two lepidopterous insects as compared with all five homopterous insects. The very low microsomal monooxygenase activity in the sucking insects may be due to their contact only with water-soluble materials in plant saps. The metabolic mechanisms of insecticide resistance observed in these species may reflect this fundamental difference in the makeup of detoxifying enzymes.