Bolls infested with pink bollworm larvae were collected from cotton fields in five locations in Arizona (Stanfield, Yuma, Buckeye, Parker, and Marana). Eggs were then gathered from the adult pink bollworms resulting from those collections and newly hatched larvae from those eggs were subjected to artificial diet containing doses of a purified solution of the Bacillus thuringiensis (bt) entomotoxin cryIA(c). The dosages of toxin were 0.00125, 0.0025, 0.005, 0.01, 0.02 0.04, and 0.08 µg/ml. Newly hatched larvae from two established laboratory strains, APHIS (a bt toxin susceptible strain) and SOOTY-BTX (a bt toxin resistant strain) were also exposed to the same doses of bt toxin. No mature individuals (individuals which were able to pupate) were produced from any of the native strains or from the APHIS strain at toxin doses exceeding 0.005 µg/ml. Mature individuals were found at all doses administered to the resistant strain. Some third instar larvae were found at toxin doses higher than 0.005 µg/ml, but none which completed development during the duration of the tests.