Zhao_1994_Pestic.Biochem.Physiol_49_13

Mechanisms of resistance were examined using UMC and KCM western flower thrips, Frankliniella occidentalis (Pergande), that differed in their susceptibility to diazinon by 14.2 times, with the latter strain being more tolerant. Diazinon penetration, metabolism, and excretion were faster in KCM than in UMC thrips. Metabolism of diazinon in both strains was mainly oxidative, and major metabolites cochromatographed with diazoxon, 2-isopropyl-4-methyl-6-hydroxypyrimidine, and 2-(2'-hydroxy-2'-propyl)-4-methyl-6-hydroxypyrimidine. Carboxylesterase activity in KCM thrips was significantly lower than that in UMC thrips and was 9.6 and 20.4 times less sensitive to diazoxon and eserine, respectively. Acetylcholinesterase (AChE) activity in KCM and UMC thrips was similar, but that in KCM thrips was 9.6 times less sensitive to diazoxon. Butyrylcholinesterase (BuChE) activity in the two strains was similar and was appreciably higher than AChE activity. BuChE activity in KCM thrips was 170 times less sensitive to diazoxon than that in UMC thrips. No interstrain difference in glutathione S-transferase activity was observed with 1-chloro-2,4-dinitrobenzene as substrate. Diazinon resistance in western flower thrips was due chiefly to rapid metabolism and insensitive AChE. The role of BuChE, if any, in diazinon resistance is not currently known; however, by serving as an alternate phosphorylation site, it could reduce the level of organophosphate at the AChE target in both strains.