Abstract
Water is a main factor in production of crops. Optimizing the usage of water is essential especially in Iran which is a dry and semi-dry country. Investigation on the effect of different irrigation treatments on Chilo suppressalis Walker (Lep.: Crambidae), as the most destructive rice pest, can be an efficient strategy in optimizing usage of water in Integrated Crop Management (ICM). In order to investigate on the influence of deficit irrigation on the performance of C. suppressalis, several factors including tiller number, leaf sheath infection, dead hearts and white heads were evaluated on Fajr variety. All the experiments were conducted in spring and summer of 2004 and 2005 in the Rice Research Institute of Amol base of deficit irrigation in two methods including dry seeded and transplanting. The experimental design was randomized complete block design with 7 treatments (various irrigation regimes) and 3 replications. After preparing of the nursery and paddy fields in mid May, 4 seedlings were sown in each hill with 30x30 cm interval and also for the plots 3x5 m2. The randomized samplings were conducted at three stages including three weeks after transplanting, eight weeks after transplanting and ten days before harvesting. In each stage, 5 hills were randomly selected from each plot and then infected and healthy tillers were counted. Data analysis indicated that different irrigation regimes had not significance effect on the mentioned characters in both methods, dry seeded and transplanting. Therefore, changing on the volume of used water in rice fields has not any effect on population density of C. suppressalis.

Key words: Deficit irrigation, Dry seeded, Transplanting, Chilo suppressalis, Fajr cultivar