Evaluation of some insecticides against white grub, Lepidiota masueta in Colocasia esculenta

Eight insecticides were evaluated against white grub, Lepidiota mansueta in colocasia at the farmer's field of Majuli river island. Fipronil 5 Sc @ 100 g a.i./ha treated plot registered lowest per cent of corm damage (7.02 and 6.95%), lowest grub population (3.33 and 3.00 numbers/sq.m) and highest yield (15.33 and 15.34 q/ha) during 1^st and 2^nd year respectively as compared to 20.87 and 20.43% corm damage with a corm yield of 10.38 and 10.39 q/ha. The highest B: c ratio (3.89 and 3.90) was observed in quinalphos 25 Ec@ 400 g a.i./ha followed by chlorpyriphos 20 Ec @ 400 g a.i./ha (2.90 and 2.96).