INSECTICIDE RESISTANCE IN-FIELD AND LABORATORY STRAINS OF WESTERN FLOWER THRIPS (THYSANOPTERA, THRIPIDAE)

Western flower thrips, Frankliniella occidentalis (Pergande), from 5 commercial greenhouses were resistant to diazinon, methomyl, bendiocarb, and cypermethrin, except in 2 tests with bendiocarb. When compared with the UMC-A reference strain, resistance ratios from LC(90)s (RR(90)) at 24 h 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. We also did toxicity studies on 2 laboratory strains (UMC, KCM). Compared with the UMC-A strain, RR(90)s indicated that UMC thrips were resistant to diazinon (14-fold), methomyl (3.6-fold), and cypermethrin (232-fold), but not to bendiocarb. The RR(90) 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(90) increasing from 0.4 to 14. Cross-resistance to cypermethrin also was present at the LC(50) (3.9-fold), but not at the LC(90). When compared with UMC thrips, KCM thrips also were resistant to permethrin (RR(90) = 2.5), fenvalerate (RR(90) = 3.6), DDT (RR(90) = 6.0), and imidacloprid (RR(90) = 14), but not to amitraz. Piperonyl butoxide, but not S,S,S-tri-n-butyl phosphorotrithioate, synergized the toxicity of diazinon, bendiocarb, and fenvalerate to KCM thrips.