author(s)
Kennedy Ningthoujam, Mareena Sorokhaibam, Rojeet Thangjam and GT Gujar

abstract
A number of putative Cry toxin receptors have been identified in various insect midgut epithelia, of which alkaline phosphatase activity has been proposed to be closely associated with the resistance of Helicoverpa armigera to Bt toxin. In the present study, midgut brush border membrane vesicles (BBMV) preparations from resistant and susceptible population of H. armigera were assayed for marker enzyme specifically alkaline phosphatase so as to understand the association of the levels of alkaline phosphatase activity and the expression of Cry 1Ac resistance. Also, the association of the levels of alkaline phosphatase activity in relation to the mode of inheritance of Cry1Ac through their F₁, backcrosses and F₂ progenies were examined. Identification and characterization of Cry toxin receptors in the midgut of H. armigera has a very important role in clarifying the Bt toxicology and its resistance mechanism so as to sustain long term use of Bt cotton. In our study, the specific acitivity of alkaline phosphatase was 108.10 and 160.93 µM/min/µg of protein, respectively for resistant and susceptible population. Alkaline phosphatase activity was observed to be more in Cry1Ac susceptible population as compared to the resistant population. The mean larval alkaline phosphatase of the resistant and susceptible parents (p=0.025) differed significantly, thus suggesting the association of decreased APN activity in resistant population. Maternal effects on inheritance of Cry1Ac resistance development was observed in F₁ progenies while nuclear effect was observed in backcrosses and F₂ progenies. Hence, it became clear from the study that the Cry1Ac resistance in the H. armigera population is conferred by alteration of the larval midgut binding to the Cry toxins.