Insecticidal activities of Azadirachtin (15% EC) were investigated on larval and pupal stages of lesser pumpkin fly, Dacus ciliatus. The mortality was recorded after 24h post-treatment. The third instar larvae more susceptible to this Azadirachtin formulation (LC50 = 23.74 ppm) than the pupal stage (LC50 = 49.97 ppm). Insects emerged with crumpled, distorted wings also female insects show swollen abdomen and deformed ovipositor after treatment of pupae with median lethal concentration. Treatment of third larval instar with median lethal concentration induced histological alterations in the cuticle and digestive system. Complete disintegration in epicuticle in some regions. The appearance of vacuoles between cuticle and epidermis has been observed. Destruction of muscular cells and fragmentation of muscular layers observed. The gastric caecal cells show serious damage, some cells appear hypertrophied, some cells have vacuoles and the lumen and intercellular spaces enlarged. Treatment-induced severe effect on the mid-gut where destruction of muscular cells and detachment of the basement membrane and muscle layers observed. The brush border of Malpighian tubules showed coagulation and detachment from epithelial cells.