MECHANISMS ASSOCIATED WITH DIAZINON RESISTANCE IN WESTERN FLOWER THRIPS

Mechanisms of resistance were examined using UMC and KCM western flowe r thrips, Frankliniella occidentalis (Pergande), that differed in thei r susceptibility to diazinon by 14.2 times, with the latter strain bei ng more tolerant. Diazinon penetration, metabolism, and excretion were faster in KCM than in UMC thrips. Metabolism of diazinon in both stra ins was mainly oxidative, and major metabolites cochromatographed with diazoxon, 2-isopropyl-4-methyl-6-hydroxypyrimidine, and '-hydroxy-2'- propyl)-4-methyl-6-hydroxypyrimidine. Carboxylesterase activity in KCM thrips was significantly lower than that in UMC thrips and was 9.6 an d 20.4 times less sensitive to diazoxon and eserine, respectively. Ace tylcholinesterase (AChE) activity in KCM and UMC thrips was similar, b ut that in KCM thrips was 9.6 times less sensitive to diazoxon. Butyry lcholinesterase (BuChE) activity in the two strains was similar and wa s appreciably higher than AChE activity. BuChE activity in KCM thrips was 170 times less sensitive to diazoxon than that in UMC thrips. No i nterstrain difference in glutathione S-transferase activity was observ ed with 1-chloro-2,4-dinitrobenzene as substrate. Diazinon resistance in western flower thrips was due chiefly to rapid metabolism and insen sitive AChE. The role of BuChE, if any, in diazinon resistance is not currently known; however, by serving as an alternate phosphorylation s ite, it could reduce the level of organophosphate at the AChE target i n both strains. (C) 1994 Academic Press, Inc.