The biochemical basis of malathion resistance in the sheep blowfly,Lucilia cuprina |
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| Institution: | 1. College of Plant Protection, Shanxi Agricultural University, Taiyuan, Shanxi 030031, China;2. Shanxi Key Laboratory of Integrated Pest Management in Agriculture, Taiyuan, Shanxi 030031, China;3. State Key Laboratory of Sustainable Dryland Agriculture (in preparation), Shanxi Agricultural University, Taiyuan, Shanxi 030031, China;4. Guangdong Key Laboratory of Integrated Pest Management in Agriculture, Guangdong Public Laboratory of Wild Animal Conservation and Utilization, Institute of Zoology, Guangdong Academy of Sciences, Guangzhou, China;5. Sorghum Research Institute, Shanxi Agricultural University, Jinzhong, Shanxi 030600, China;6. College of Plant Protection, China Agricultural University, Beijing 100193, China;1. Key Laboratory of Entomology and Pest Control Engineering, College of Plant Protection, Southwest University, Chongqing 400715, China;2. Key Laboratory of Agricultural Biosafety and Green Production of Upper Yangtze River (Ministry of Education), Southwest University, Chongqing 400715, China;3. National Citrus Engineering Research Center, Southwest University, Chongqing 400715, China;4. Department of Mathematics and Statistics, Southwest University, Chongqing 400715, China |
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| Abstract: | The in vivo and in vitro metabolism of 14C]malathion was studied in susceptible (LS) and malathion resistant (RM) strains of the sheep blowfly, Lucilia cuprina (Wiedemann). No difference was found between strains in the penetration, excretion, storage, or inhibitory potency of the insecticide. However, RM degraded malathion to its α- and β-monocarboxylic acid metabolites more rapidly than LS, both in vivo and in vitro. This enhanced degradation of 14C]malathion occurred in vitro in both mitochondrial and microsomal fractions of resistant flies. Kinetic analysis revealed that these fractions degraded malathion by discrete mechanisms. The enzymes from the mitochondria of both strains had the same Km, whereas the microsomal enzyme from the RM strain had a fivefold higher Km than that from the LS strain. Studies of esterase activities and the effect of enzyme inhibitors showed that both the mitochondrial and microsomal resistance mechanisms were the result of enhanced carboxylesterase activity. It was concluded that increased carboxylesterase detoxification of malathion adequately explained the high level of malathion resistance in RM if rate-limiting factors such as cuticular penetration were taken into account. |
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