Base-line data were obtained on beet armyworm populations from the Yaqui, valley of Sonora, Mexico in response to emamectin benzoate. This is a new insecticide with a different mode of action, related to the avermectin family. Field collected populations from cotton and chili were compared to a susceptible and a colony reared for one year under laboratory conditions. Bioassays were performed on third instar larvae weighing 20-25 mg, at least 250 larvae from the first to the third generation after field collection were used in each bioassay. Each larvae was treated with one microliter of a solution of technical grade emamectin benzoate dissolved in acetone. Five to seven concentrations were used in each bioassay. Mortality data was obtained 48 hours after topical application of the insecticide, data was corrected for control mortality (never >10%) using Abbot´s formula, then analyzed by the probit model, significant differences 95% were considered only if fiducial limits of the LD₅₀ values do not overlap. Results showed a LD₅₀ value of 0.68 g/g and fiducial limits ranging from 0.36 g/g to 1.41 g/g, in the susceptible colony, which are similar to those in the LAB-95 and field collected colonies of beet armyworm. The LAB-95 colony can be used as a reference colony to measure any change in response of beet armyworm populations in Mexico. These data indicate susceptibility of the colonies evaluated and represent base lines for emamectin benzoate in beet armyworm populations in Mexico.