RESISTANCE TO INSECTICIDES IN POPULATIONS OF FRANKLINIELLA-OCCIDENTALIS (PERGANDE) (THYSANOPTERA, THRIPIDAE) FROM GREENHOUSES IN THE NIAGARA REGION OF ONTARIO

Resistance was documented in 1995 to commonly used organophosphorus, c arbamate, and pyrethroid insecticides in populations of western flower thrips, Frankliniella occidentalis (Pergande), from six commercial gr eenhouses in Ontario. Adult female thrips were placed in glass vials t reated with technical-grade insecticides and mortality at 18 h was com pared with a single discriminating concentration, the computed LC99 of a reference laboratory population. Baseline dose-response regressions for insecticides commonly used in Ontario greenhouses were obtained f or the laboratory population of western flower thrips. The organophosp horus compounds chlorpyrifos and malathion and the carbamates methomyl and bendiocarb were the most toxic materials tested; whereas the pyre throid deltamethrin and a phosphoroamidate acephate were the least tox ic. The addition of piperonyl butoxide to solutions of deltamethrin wa s highly synergistic. The mixture of deltamethrin and endosulfan (1:1) was moderately synergistic. Populations of western flower thrips from commercial greenhouses were resistant to deltamethrin, but deltamethr in mixed with piperonyl butoxide or endosulfan was synergistic in all cases. None of the populations were resistant to all of the insecticid es tested. Recommendations are presented for the development of a resi stance-management strategy for western flower thrips.