QUANTIFICATION OF INSECT PEST AND NATURAL ENEMY INCIDENCE VIS A VIS YIELD

A quantification study on insect pests and natural enemies incidence in rainfed rice in Assam was carried out during the sali season of 2000. Estimation of insect pest and natural enemy populations was done under three treatments viz. Need Based Pesticide application (NBP), Natural Biological control (NBC) and Scheduled Based Pesticide (SBP) application in ten farmers fields in five villages of Jorhat and Golaghat districts of Assam. The results revealed that SBP resulted in significantly lower stem borer damage compared to NBP and NBC, while insecticidal application did not have significant effect on leaf folder incidence upto 60 DAT. However, at 75 DAT, SBP showed significantly less incidence of leaf folder compared to NBP and NBC, which were at par. SBP also resulted in lower gall midge incidence but at 60 DAT, NBP recorded less damage by gall midge due to the application of pesticide at 50 DAT in the NBP treatment. Population of predators viz. spiders, coccinellids, dragonflies and damselflies were lowest in SBP, and highest in NBC. In terms of grain yield and economics, despite highest yields in SBP, the NBP treatment was the best treatment as it showed highest Cost Benefit Ratio (CBR) and could harbour more natural enemies.