Variation in brush border membrane vesicle receptors and activity of proteolytic enzymes in relation to toxicity of Bt toxins to Helicoverpa armigera larvae

Abstract

Mechanism involved in development of resistance in Helicoverpa armigera larval populations from nine locations was evaluated by performing; a) in-vitro binding assays with Brush border membrane vesicle receptors and trypsin activated Bt toxin Cry 1Ac and b) by performing SDS-PAGE with activated toxin and gut juices of H. armigra populations form nine locations. Our results demonstrated that resistance/lower sensitivity of Mahabubnagar and Parbhani H. armigera larval populations (LC90 values 10.2851 and 15.6230 µg ml-1) to Bt toxins was due to reduction in proteolytic activity of gut extract results in production of less activated toxin and degradation of the activated toxin to a relatively less toxic product. Resistance of Nanded population (LC90 value 13.7219 µg ml-1) was due to low amount of the activated toxin produced from the protoxin. In case of Bidar and Kurnool populations, their relative sensitivity to Bt (LC90 values 4.0434 and 5.7445 µg ml-1, respectively) was due to high binding ability of activated toxin to Brush border membrane vesicle receptor proteins of midgut epithelial cells (137 7 135 µg g-1).