Feeding behaviour of chrysomelid leaf beetles Aplosonyx chalybaeus (Hope) and A. scutellatus (Baly)

Two chrysomelid leaf beetles, Aplosonyx chalybaeus (Hope) and A. scutellatus (Baly) (Galerucinae: Chrysomelidae) are endemic to the northeast Indian hills and adjoining areas where their host plant, Colocasia esculenta (L.) Schott originated. This study brings out the feeding behaviour of these. The univoltine life cycle of these beetle is in close synchrony with the phenology of their host plant C. esculenta. The creamy white ‘caterpillar-like’ grubs from first to the fourth instar feed gregariously inside the long petioles and sometimes enter the underground tubers. The final instar grubs invariably bore into the tuber and feed inside. Due to the feeding and movements of a group of 15–20 grubs, the internal starchy contents of the tuber get loosened. The final instar make vigourous churning movements within the tuber and this often leads to the starchy contents become a thick viscous milky fluid. Thus the final instar grubs live in a fluid environment till they get dispersed for pupation underground. The adult beetles exhibit leaf trenching behaviour to drain off the milky latex from the leaf canals before feeding. The feeding results in circular or elongated holes in the leaf. The beetle feeds the leaf at a very early stage of trenching. Lack of turgor pressure in the leaf veins could be the reason for early discontinuance of trenching on severed leaf. Time taken to make circular trench and feeding hole on the leaves and the area of leaf consumed by adults is discussed.