Azadirachtin-based insecticides induce alteration in Helicoverpa armigera Hub. head polypeptides

Azadirachtin obtained from seed kernel of Indian neem (Azadirachta indica A. Juss) is a plant-based insecticide for field-crop applications. Helicoverpa armigera Hub. (Lepidoptera: Noctuidae) is one of the most destructive and highly polyphagous insect pests of field crops and has developed resistance against most of the modern classes of synthetic insecticides worldwide. The ultimate instars of H. armigera larvae treated topically with 10 ppm of three azadirachtin-rich neem formulations, viz. Achook, Nimbicidine and Neem Jeevan, were found to significantly (P < 0.05) reduce total head protein after 0, 24, 48 and 72 h of treatment application over control. Achook in 24 h and Neem Jeevan in 48 and 72 h exhibited significantly (P < 0.05) reduced protein level compared to Nimbicidine and control. Azadirachtin applied by injection method in third instar larvae significantly (P < 0.05) reduced protein level at higher dose (5 μl). Similar trend was found in larvae of fourth instar. Diet mixed with different azadirachtin-based formulations and fed to fourth instar larvae of H. armigera also significantly (P < 0.05) reduced protein level. The experimental results also indicated that serial dilutions of both azadirachtin and Nimbicidine treatment resulted in significant (P<0.05) negative response to various doses by injection as well diet-fed method respectively. SDS-PAGE analysis of proteins showed that azadirachtin suppressed 22, 26, 40 and 56 kDa head polypeptides in various treatments. However, haemolymph injection of azadirachtin (10 ppm) into third and fourth instar larvae of H. armigera reduced the total head protein level below that of control larvae and altered the polypeptide pattern. Alteration in SDS polypeptide pattern was also observed with different modes of application in a dose-dependent fashion.