Study on Larvicidal Effect of Different Plant Parts of Milk Weed Plant (Calotropis gigantea R. Br.) against Helicoverpa armigera

The larvicidal property of aqueous extracts of different plant parts of milk weed plant viz., leaves, stem, flower and roots were studied on III, IV, V instar larval stages of the Helicoverpa armigera at two, four, six, eight and 10 per cent concentrations. The results indicated the five plant parts extract caused significant larval mortality. But the mortality was the maximum (80.00%) when aqueous leaf extract at 10 per cent concentration was used on second instar larvae of H. armigera. The mortality rate was high in second instar larvae and gradually decreased in the third, fourth and fifth instars larvae. As the larvae became older, the mortality was nil in the fifth instar larvae. In leaf extract, the mortality per cent got reduced from 83.33 to 76.66 per cent in third instar and 63.33 per cent in fourth instar. The flower extract was treated on different larval instars at various concentrations and from the results, it was observed that 10 per cent extract caused larval mortality to an extent of 66.66, 53.33 and 20.00 per cent on third, fourth and fifth instars respectively. The root extract was less effective and caused 36.66 per cent mortality in second instar. This percentage got reduced when it was treated on the succeeding larval instars, namely third, fourth and fifth instar. The whole plant extract showed greater mortality next to leaf and flower extract at 10 per cent concentration and caused larval mortality to an extent of 63.33, 46.66 and 16.66 per cent on third, fourth and fifth instar.