RESPONSE TO INSECTICIDES BY FOUR CROSSES OF BEET ARMYWORM(LEPIDOPTERA: NOCTUIDAE) STRAINS FROM NORTH AMERICA

摘要

Larvae from four crosses of three field collected strains of beet armyworm (Spodoptera exigua (Hubner)) (BAW) from FLand TX, United States of America (USA) and northern Tamaulipas, Mexico were treated with 14 insecticides for one, twoand 10 generations. An LD50s of 20 μg/larva was used as a resistance threshold to separate resistance from susceptibility.Cypermethrin showed selection for resistance in the cross of the three strains, while the other crosses and the three straincross showed cross and multiple resistance and reversion to susceptibility. Susceptibility was shown to bifenthrin, chlorpyrifos,deltamethrin, zeta cypermethrin, fenpropathrin, lambda cyhalothrin and chlorphenapyr by the Alva x Donna and the Alvax Donna x Rio Bravo crosses. Crosses of strains of the BAW can be resistant to one insecticide one generation yet be susceptibleto the same insecticide the next. Factors for resistance and susceptibility of these crosses have to be polygenic.