Discriminating concentrations of several standard and experimental insecticides were determined for an insecticide susceptible strain of soybean looper using an insecticide diet overlay bioassay. These concentrations were used to evaluate the relative susceptibility of field and F1 generations of three field-collected strains of soybean looper larvae. Field strains exhibited significantly higher percent survival compared to the susceptible reference strain (USDA) when exposed to Ambush^®, Condor XL^® and Larvin^® as larvae directly from the field or as F1 laboratory-reared larvae. Soybean looper larvae collected from Bt-cotton had higher survival when exposed to Condor XL^® than the USDA larvae. Larvae from field strains exposed to the discriminating concentration of Pirate^® and Proclaim^® did not exhibit significantly higher survival than that of the reference strain. In the Proclaim^® bioassays, larval survival for two field strains of the field generation was significantly lower than that of the reference strain. In the Tracer bioassays, two strains in the field generation bioassays and one strain in the F1 generation bioassay had survival significantly higher than the USDA strain. These differences may have been due to natural variation in the soybean looper population, but need further investigation.