AbstractToxicity of a neem seed kernel extract (AZAL‐S) was assessed under laboratory conditions against larvaeof Culex quinquefasciatus. The LC50value for AZAL‐S was 0.78× 10–6. Exposure of 4th instar larvae to 0. 3× 10–6 and 0. 5× 10–6 AZAL‐S for 120 hours caused 46. 2% and 67. 5% mortality respectively, with various types of morphogenetic aberration. AZAL‐S induced an obvious prologation of the larval period when 1st instar larvae were treated with 0. 4–1. 0× 10–6 AZAL‐S for 7 days. The insect growth regulating effect of AZAL‐S on mosquito larvae was similar to those reported for certain