Laboratory studies were conducted to evaluate the behavioral response of bollworm and fall armyworm on non-Bt cotton cultivars versus those expressing one (Bollgard ^J ) or two (Bollgard II ^J ) insecticidal proteins of Bacillus thuringiensis. Plastic trays consisting of cells with interconnecting corridors were used to assay larval movement and preference for meridic diet containing freeze-dried leaf tissue. After six hours, there was no significant difference in the variety bollworm or fall armyworm larvae preferred. For all varieties, 75-84% specimens were still in cells containing diet with incorporated leaf tissue. However, only 28% of bollworm larvae had moved from their original cell containing non-Bt tissue, compared to 49% that had vacated cells containing either Bt cotton tissue. About 60% of fall armyworm larvae were found in cells containing non-Bt and dual-toxin tissue, and fewer were found on single-toxin tissue (43%). After 24 hours, 88% of bollworms were found in cells containing non-Bt plant tissue, compared to 68% and 53% of bollworms found in cells containing single-toxin and dual-toxin plant tissue, respectively. Fall armyworms were found in cells containing tissue from non-Bt and single-toxin cotton 61% and 71% of the time, respectively. Only 36% of fall armyworms were found in cells containing both Cry1Ac and Cry2ab toxins. Larvae of both bollworm and fall armyworm were more inclined to move when placed in cells containing dual-toxin Bt plant tissue, as 78% of the larvae moved at least one cell after 24 hours. Approximately 50% of larvae moved when placed in cells containing non-Bt and single-toxin plant tissue.