Susceptibility of field populations of beet armyworm (Lepidoptera: Noctuidae) to cyfluthrin, methomyl, and profenofos, and selection for resistance to cyfluthrin

The tolerance of the beet armyworm, Spodoptera exigua (Hubner), to 3 insecticides-cyfluthrin, methomyl, and profenofos-was investigated in 2 field strains collected from Marana and Yuma, AZ. The susceptible laboratory strain was obtained in California. Dose-mortality data were obtained by topical application on 3rd instars. Compared with the susceptible strain, the Marana and Yuma strains exhibited resistance ratios of 5.5 and 15.7 to cyflutrin, 8.1 and 3.0 to methomyl, and 17.8 and 14.1 to profenofos, respectively. Selection of the Marana stain for resistance to cyfluthrin for 8 generations resulted in a 54.1-fold increase in the LD(50). The selected strain was then tested for cross resistance to methomyl and profenofos. Resistance to methomyl increased by 24.7-fold, whereas resistance to profenofos increased only 3.3-fold in the cyfluthrin-selected strain.