Studies on the biology of an important forest plant defoliator Eligma narcissus on Ailanthus spp (economically important forest plant yielding raw material for paper manufacture and aromatic resins). Ecological relationships of this pest species with reference to climatological factors in man-made plantations presented. Influence of host plants on its survival and reproduction, lifetables are presented. This is a monograph on Eligma narcissus covering major aspects and I feel its a useful reference for researchers in Entomology.