Bio-efficacy of ‘Neem Azal’ (azadirachtin 10,000 ppm) against cotton bollworm, Helicoverpa armigera Hubner

Bio-efficacy of Neem Azal was studied against the insecticide-resistant populations of Helicoverpa armigera Hub. The effects of this new botanical neem formulation on larval growth and development were quite significant. The LC50 values for neonate and the second instar larvae were 0.002 and 0.004%, when fed on Neem Azal treated cotton leaves continuously. However, the LC50 values were 0.005, 0.02 and 0.03% for the I, II and III instar larvae of H. armigera when the exposure was limited to 48 h. Also, the neonate and second instar larvae were exposed to different concentrations of azadirachtin and the growth effects were estimated until pupal stage. Of the different concentrations, the highest dose of 0.04% proved to be the most toxic by recording 100 per cent mortality. The mean larval weight was 191.6 g when maintained on treated (200 ppm) leaves as compared to 337.8 g on normal leaves. The reduction in azadirachtin concentration improved the larval and pupal weights considerably. Even, the lowest concentrations, viz., 0.000625 and 0.0003125 per cent showed phagostimulant effects, the larval weights being 245.3 and 249.6 g as against 244.6 g in the control larvae. However, the growth disrupting effects were clearly evident with increasing dosages. Neem Azal, too, affected the pupal weight besides resulting in the formation of deshaped structures by incomplete metamorphosis.