Bollworm, Helicoverpa zea (Boddie) and tobacco budworm, Heliothis virescens F. eggs, larvae and adults were collected in geographically diverse regions of Arkansas from April to September 2005. Adult moths were collected from light traps, and eggs and 1st to 5th instars larvae were collected on non-cultivated and cultivated host plants. More than 100 field populations were established. Resulting colonies were assayed for susceptibility to Cry1Ac using a diet incorporation assay. Variability in assay results are being studied by host plant of collection, geographic location of collection, and relative time during the season to explore influences on field selection for resistance to the insecticidal protein. Results will be discussed.