Male and female nymphs of Heteracris littoralis were topically treated with serial concentrations of azadirachtin. Effects on mortality, development, oogenesis and spermatogenesis were observed. Mortality was dose-dependent; fourth and fifth instars died about the time of ecdysis. Overaging took place at low concentrations. Ovaries in treated adult females showed complete shrinkage with abolished oocyte growth, and the number of deposited egg pods/female decreased from 4 to 9 in normal females, to 1 to 3 pods in treated insects. Deformation in sperm tubes was observed in treated males. Electronmicrographs revealed disintegration and destruction in follicular cells and mitochondria in females. In males the testicular epithelia and the spermatids completely disintegrated. Treatment with higher doses inhibited cyst formation around the spermatogonia.