Four experiments were carried out at Sakha Agricultural Research Station during 1995 and 1996 seasons to study the influence of four water regimes on cotton infestation by pink bollworm, Pectinophora gos­sypiella and spiny bollworm, Earias insulana as well as on cotton yield. The results indicated that the highest infestation by both insects was obtained when cotton plants were irrigated every two weeks throughout the growing season. The least infestation was for three week intervals. Also, larval population of both insects took the same trend. Significant influence of irrigation intervals were found on both number of open bolls and seed cotton yield. The highest number of open bolls and cotton yield were recorded when cotton plants were irrigated every two weeks during vegetative growth stage and three weeks during fruiting stage. This water regime supplies the plants with sufficient wa­ter during vegetative stage, and keeps the water table at low level at fruiting stage. So, this treatment could be recommended to : (1) reduce bollworm infestation, (2) save water irrigation and (3) get higher cotton yield.