Toxic effects of neem based insecticides on the fitness of Helicoverpa armigera (Hübner)

The toxic effects of neem based insecticide products (Neemarin (0.15% EC azadirachtin), Neemazal (1% EC azadirachtin), Neemix (0.25% EC azadirachtin) and Neem oil (1% EC azadirachtin)) were evaluated on Helicoverpa armigera (Hübner) using a life table approach. Additional studies were done to determine the effects of the neem insecticides on the development time of immature stages. The survivorship was maximum (46 days) for Neemazal treated groups and 42 days in untreated groups. Life expectancy was highest (26.3 days) with Neem oil at very first day of age while it was 19.9 in controls. All the eggs hatched when treated with Neemarin, Neem oil and control while, 94% hatched when treated with Neemazal. The potential fecundity was lowest with Neemix (378 females/female/generation) and highest in the untreated control (1034). Daily fecundity rate (mx) was significantly greater (143 offspring/day) in the control than 58 offspring/day with Neemazal. Intrinsic rate of increase was lowest (0.026 day−1) with Neemazal as compared to unexposed groups (0.041 day−1). The time taken to complete one generation was 38.8 days in untreated groups, while it was prolonged to 40.6 days with Neemazal and reduced to 37.4 days with Neemarin. Doubling time was prolonged to 11.7 days with Neemazal while it was 6.4 days in unexposed groups. Development of immature stages was increased to 37.6 days with Neemazal while reduced to 32.3 days with Neemix as compared to 35.6 days in unexposed controls. It is concluded that the different neem insecticides had widely varying adverse effects on the fitness parameters of H. armigera. Impacts such as reduction in fecundity, reproductive rates, immature development and adult emergence may change the occurrence period of this pest in relation to crop and the crop may be escaped pest damage. Hence, are suitable for integration into an IPM program of this pest.