Neem seed kernel extracts adversely affect the growth and morphogenesis of insects. InTrogoderma granarium, neem seed kernel extract was found to inhibit normal pupal-adult development. The malformed adults comprised a heterogenous group of transitory forms between the pupal and adult types. Older pupae were less sensitive to the compound. In the seemingly normal surviving adults ofTrogoderma granarium a reduction in the number of vitellogenic oocytes was found. The active compound(s) in the neem seed kernel extracts is proposed to produce the observed effects by regulating morphogenetic hormone titres, though the precise mode of action cannot be safely defined.