Enhanced metabolism and knockdown resistance in a field versus a laboratory strain of the soybean looper (Lepidoptera: Noctuidae)
1990
Soybean looper, Pseudoplusia includens (Walker), larvae collected from a field where permethrin failed to provide adequate control and for which a reduction in susceptibility to permethrin had been demonstrated (3-fold at LC50) were compared with an established laboratory colony with respect to knockdown resistance (kdr) and in vitro metabolic capacity for a variety of substrates. The time necessary to achieve 50% knockdown of the field population (22.9 +/- 1.3 min) after the topical application of 1 microgram permethrin was significantly greater than that required for the laboratory colony (18.4 +/- 1.0 min). Rates of metabolism for first-generation larvae from the field population were significantly greater than for larvae from the laboratory culture for substrates of glutathione transferase (1-chloro-2,4-dinitrobenzene, 2.7-fold), monooxygenases (p-nitroanisole O-demethylase, 1.8-fold), and hydrolases (alpha-naphthyl acetate [1.5-fold], p-nitropheny) acetate [1.5-fold], and permethrin [1.5-fold]). Significant differences between populations were not observed for NADPH cytochrome c reductase nor acephate hydrolysis. Results of the study indicate that a combination of target site insensitivity and increased activity of several enzymes involved in insecticide metabolism including a trans-permethrin hydrolase may be contributing to the reduced susceptibility of the field population relative to the laboratory colony.
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