Detection of and mechanisms associated with resistance of western flower thrips, Frankliniella occidentalis (Pergande), to insecticidal esters

Western flower thrips, Frankliniella occidentalis (Pergande), from five commercial greenhouses were resistant to diazinon, methomyl, bendiocarb, and cypermethrin, with the only exceptions being two tests with bendiocarb. When compared with the UMC-A reference strain, resistance ratios from LC{dollar}sb{lcub}90{rcub}{dollar}s (RR{dollar}sb{lcub}90{rcub}{dollar}) at 24 hours ranged from 10.4 to 98 for diazinon, 3.4 to 26 for methomyl, 0.9 to 11 for bendiocarb, and 18.3 to 273 for cypermethrin. Toxicity studies also were done on two greenhouse strains of F. occidentalis (UMC, KCM). When compared with the UMC-A strain, RR{dollar}sb{lcub}90{rcub}{dollar}s revealed that UMC thrips were resistant to diazinon (14-fold), methomyl (3.6-fold), and cypermethrin (232-fold), but not to bendiocarb. The RR{dollar}sb{lcub}90{rcub}{dollar} of KCM thrips reared under diazinon selection increased from 4.0 to 271 when compared with UMC-A thrips. During diazinon selection, cross-resistance to bendiocarb was evident, with the RR{dollar}sb{lcub}90{rcub}{dollar} increasing from 0.4 to 14. Cross-resistance to cypermethrin also was present at the LC{dollar}sb{lcub}90{rcub}{dollar} (3.9-fold) but not at the LC{dollar}sb{lcub}90{rcub}.{dollar} When compared with UMC thrips, KCM thrips also were resistant to permethrin (RR{dollar}sb{lcub}90{rcub}{dollar} = 2.5), fenvalerate (RR{dollar}sb{lcub}90{rcub}{dollar} = 3.6), DDT (RR{dollar}sb{lcub}90{rcub}{dollar} = 6.0), and imidacloprid (RR{dollar}sb{lcub}90{rcub}{dollar} = 14), but not to amitraz. Piperonyl butoxide, but not DEF, synergized the toxicity of diazinon, bendiocarb, and fenvalerate to KCM thrips.; Mechanisms of resistance were examined using UMC and KCM thrips that differed in their susceptibility to diazinon, bendiocarb, and fenvalerate at the LC{dollar}sb{lcub}90{rcub}{dollar} by 12-, 14-, and 7-fold, respectively, and at the LC{dollar}sb{lcub}90{rcub}{dollar} by 22-, 45-, and 4-fold, respectively. It was concluded that resistance of western flower thrips was due to enhanced metabolism and insensitive acetylcholinesterase in the case of diazinon, to enhanced metabolism in the case of bendiocarb, and to reduced penetration and enhanced metabolism in the case of fenvalerate.; These studies have confirmed the presence of resistance in western flower thrips from commercial greenhouses in Missouri to organophosphate, carbamate, and pyrethroid insecticides. Multiple resistance mechanisms including both pharmacokinetic and pharmacodynamic types were present.