The biochemical basis of resistance to organophosphorus insecticides in the sheep blowfly, Lucilia cuprina |
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| Authors: | PB Hughes AL Devonshire |
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| Institution: | 1. Biological and Chemical Research Institute, New South Wales Department of Agriculture, Rydalmere, 2116, Australia;2. Department of Insecticides and Fungicides, Rothamsted Experimental Station, Harpenden, Hertfordshire, United Kingdom |
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| Abstract: | The metabolism in vivo and in vitro of 14C]parathion and 14C]paraoxon was studied in a susceptible (LS) and an organophosphorus-resistant (Q) strain of the sheep blowfly, Lucilia cuprina. Both strains detoxified the insecticides in vivo via a number of pathways, but the resistant strain produced more of the metabolites diethyl phosphate and diethyl phosphorothionate. No difference was found between strains in the rate of penetration of the compounds used. Also, in vitro studies showed no difference between strains in the sensitivity of head acetylcholinesterase to inhibition by paraoxon. Both the microsomal and the 100,000g supernatant fractions degraded paraoxon, but resistance in Q could be explained by the eightfold greater rate of diethyl phosphate production with or without added NADPH. Parathion was also degraded to diethyl phosphorothionate by an NADPH-requiring enzyme in microsomal preparations from both strains. However, Q produced significantly more diethyl phosphorothionate in vivo than LS. It was concluded that organophosphorus resistance in Q was due mainly to a microsomal phosphatase hydrolyzing phosphate but not phosphorothionate esters, probably enhanced by a microsomal oxidase detoxifying the latter. |
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