TOLERANCE TO CYPERMETHRIN AND ENDOSULFAN IN-FIELD POPULATIONS OF THE BOLLWORM (LEPIDOPTERA, NOCTUIDAE) FROM TEXAS

Responses to insecticides in bollworm, Helicoverpa tea (Boddie), males collected from 1988 to 1994 in sex-pheromone baited traps in the Braz os Valley near College Station, TX, varied during each season with tol erance being highest in midseason. Significant tolerance occurred with cypermethrin in 1988 and 1989, and with endosulfan in 1994. Tests in 1994 with profenofos or methomyl showed no significant tolerance to th ese insecticides. We found significant variations between trap sites i n responses of field bollworms to cypermethrin, suggesting that increa sed tolerance may be a localized phenomenon. Tests with cypermethrin p lus piperonyl butoxide indicated significant synergism in bollworms co llected from the field, suggesting that enhanced metabolic degradation may be a factor in pyrethroid tolerance in this species. Diagnostic c oncentrations for monitoring tolerance in field-collected bollworm mal es were determined for all insecticides tested, The results reported h ere validate use of the adult vial test to monitor for tolerance to in secticides in the bollworm, and provide information useful for the dev elopment of a resistance management strategy intended to extend the ef ficacy of insecticides used to control the bollworm.