Preliminary trials were conducted in the laboratory and field to determine if lower rates of insecticides could be utilized to control bollworms "coming through" in B.t. cotton. Larvae exposed to Dipel®-impregnated diet were significantly smaller and more susceptible to cyhalothrin (Karate®) than larvae exposed to non-Dipel® diet. Dipel® contains multiple B.t. endotoxins, in addition to the Cry IA(c) endotoxin expressed by transgenic B.t. cotton. Future studies will utilize MVP® which only contains the Cry IA(c) protein. Larvae of similar size collected from B.t. and non-B.t. cotton in the field were treated topically with cyhalothrin. Cyhalothrin concentrations were too high. As a result, LD50 values were not significant, although larvae collected from B.t. exhibited a 10-fold increase in susceptibility.