Interaction of Cry1Ac toxin (Bacillus thuringiensis) and proteinase inhibitors on the growth, development, and midgut proteinase activities of the bollworm, Helicoverpa zea

Potential resistance development to Bt cotton in certain lepidopterans has prompted research to develop strategies that will preserve this environmental-friendly biotechnology. Proteinase inhibitors are potential candidates for enhancing Bt toxicity against lepidopteran pests and for expanding the spectrum of control for other insects. Interactions of Bt toxin from Bacillus thuringiensis and proteinase inhibitors were investigated by monitoring growth, development, and gut proteinase activities of the bollworm, Helicoverpa zea. Several proteinase inhibitors were combined with Bt protoxin Cry1Ac in artiWcial diet and fed to newly molted 3rd-instar bollworm larvae to determine eVects on larval body weight and length, pupation progress, and mortality rate. Major midgut proteinase activities, including caseinase, tryptic, and chymotrypsin activities, were examined after treatment. A concentration of Bt at a level causing minimal mortality (<10%), was mixed with the following proteinase inhibitors: benzamidine, phenylmethylsulfonyl Xuoride (PMSF), and N-tosyl-L-lysine chloromethyl ketone (TLCK). When compared with controls, the synergistic eVect of Bt toxin and proteinase inhibitors caused signiWcant decreases in mean larval weight and length over time. Midgut samples tested against the substrates azocasein, -benzoyl-DL-arginine-pnitroanilide (BApNA), and N-succinyl-alanine-alanine-proline-phenylalanine-p-nitroanilide (SAAPFpNA) showed signiWcant decreases in the protease activity of larvae fed Bt plus inhibitor versus control. Interaction of Bt and proteinase inhibitors signiWcantly retarded larval growth and resulted in developmental delay and up to 20% mortality. © 2006 Elsevier Inc. All rights reserved.