Association of Insect Pests with Neem, Azadiracta indica with Special Reference to Biology of Ash Weevils, Myllocerus sp in Jaffna, Sri Lanka

Abstract

In spite of remarkable spectrum of activity of neem, Azadirachta indica (Family: Meliaceae) against pests, does the tree itself not immune to them. Many insects such as ash weevils, tortricid moth, peacock moth, scale and thrips were found associated with this tree in Sri Lanka. The biology of ash weevils, Myllocerus sp., was studied as heavy defoliators. Four species of Myllocerus such as M. viridis, M. discolor, M. subfaciatus and M. maculosus were found damaging the leaves. Adults of Myllocerus sp were small and had a dense covering of greyish to green with black cuticular marks. Female weevils laid eggs in clusters of 35.16±7.13 on muslin cloth covered the rearing chamber. Fecundity of weevil was 237.5±30.4 eggs. The mean incubation period of egg was 4.57±0.53 days at 28.9±1°C. The percent hatchability of egg was 68.12±11.15 at 28.9±1°C. The neonate grubs were small, creamy white with brown head, but just prior to pupal formation they enlarged in size. They burrowed through the soil and fed on the rootlets of Vernonia cinerea. The mean grub period was 50.6±1.51 days at 29.1±1°C. Pupation was observed in an earthen brown coloured puparium. Mean pupal period was 7.83±0.75 days at 29.1±1°C. V. cinerea is the highly preferred weed hosts of Myllocerus sp. The dicot weed was served an identical breeding site there by facilitating the survival and development of weevils through out the year. Because the leaves of V. cinerea were fed by adult weevils whilst grubs fed on its rootlets.