Differences in larval midgut protease activity between Cry1Ac-resistant and susceptible strains of Helicoverpa zea

Large-scale planting of transgenic Bt crops has led to field-evolved resistance in several key target pests including the corn earworm (Helicoverpa zea) in the southeastern United States. To explore the role of proteases in resistance to Bt toxin Cry1Ac in H. zea, we compared the protease activities of the soluble fractions of larval midgut extracts between Cry1Ac-resistant and susceptible strains. The results show that total proteolytic activity, trypsin-like protease activity, and chymotrypsin-like protease activity were higher in the susceptible strain than in the resistant strain.