Responses of Populations of the Tobacco Budworm (Lepidoptera: Noctuidae) from Northwest Mexico to Pyrethroids

Abstract

Dose-mortality bioassays were begun in 1984 to determine the susceptibility of the tobacco budworm, Heliothts virescens (F.), to commonly used pyrethroids. Responses of different populations from the northwestern region of Mexico were compared with responses of two susceptible strains. The LD50’s indicated that the populations have been and are being selected for resistance to varying degrees. A population from Valle de Mexicali had the highest LD50 and resistance ratio for deltamethrin. The highest LD50’s for permethrin were obtained from 1987 populations from Valle del Yaqui and Valle de Mexicali (resistance ratios of 55.4 and 48.7, respectively). Resistance ratios from Valle del Yaqui for cypermethrin indicated that the 1987 tobacco budworm population was 32 times more resistant than the susceptible colony. Although control failures have not been reported from these areas, the dose-mortality data suggest that control failures may occur. Permethrin resistance appears to be increasing in Valle del Yaqui, Costa de Hermosillo, and Valle de Mexicali. Resistance to cypermethrin and cyfluthrin seems to be increasing in Valle del Yaqui and Valle de Mexicali. On the basis of LD50’s, deltamethrin resistance remains low except for Valle de Mexicali but should be carefully monitored.