Influence of Bacillus thuringiensis toxins on the development and midgut proteases in different larval instars of Helicoverpa Armigera Visweshwar R2, Akbar S.M.D2, Sharma H.C.2, Sreeramulu K.1,* 1Department of Biochemistry, Gulbarga University, Kalaburagi, 585106, Karnataka 2Department of Entomology, International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, 502324, Telangana *Corresponding author Email: ksramu@rediffmail.com
Online published on 23 October, 2018. Abstract Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most important pest worldwide. Bacillus thuringiensis (Bt) toxins have used as a biopesticide or deployed in transgenic plants for controlling this pest. We examined the biological activity of Cry1Ac, Cry1Ab and Bt formulation in different larval instars of H. armigera with respect to larval development and proteolytic activity to pinpoint the most susceptible instar, and the insect response to ingestion of Bt toxins. In the presence of Bt toxins, the larval mortality and weight loss increased in a dose-dependent manner, and the maximum effect was observed in neonates. Active Cry1Ac toxin resulted in greater mortality and weight loss in all the larval instars. Total protease, trypsin and chymotrypsin activities declined in the presence of Bt toxins as compared to the untreated control in all the larval instars. Ten protease isozymes were observed in the untreated control larvae in second, third and fourth instars. Maximum protease isozymes inhibition was observed in Bt toxin fed neonates. Inhibition of protease activity increased with the concentration of Bt toxins. In presence of Bt toxins, aminopeptidase activity increased from II to IV instar and alkaline phosphatase activity decreased from II to III and then increased in IV instar. The pathogenicity of Bt was greater in early larval instars of H. armigera than the later instars, suggesting that application of Bt formulation or deployment of Bt toxins in transgenic plants should be directed against the early larval instars. Top Keywords Helicoverpa armigera, Bacillus thuringiensis toxins, larval growth and survival, proteases, aminopeptidases, alkaline phosphatases, pest control. Top |