Bioefficacy of three insecticides against tobacco caterpillar, Spodoptera litura (Fab.)

The bioefficacy of three insecticides viz. monocrotophos, indoxacarb, and chlorpyriphos was determined against 9 day old larvae of Spodoptera litura by leaf dip bioassay method. The mortality data recorded at 18, 24, 36, 48 and 72 hours after exposure (HAE) did not meet the basic requirements to go for probit analysis, therefore LC values have not been computed at these exposure periods for indoxacarb. At 24 HAE, the LC50 values of monocrotophos & chlorpyriphos were 220 & 170 ppm respectively. Chlorpyriphos showed 1.29 times more toxicity than monocrotophos at LC50 while at 34 HAE, monocrotophos showed 1.11 times more toxicity than chlorpyriphos against S. litura. In leaf dip bioassay, indoxacarb could cause 50% mortality in a shortest span of 16.64 h at 50 ppm followed by chlorpyriphos (18.06 h) at 400 ppm and monocrotophos (30.39 h) at 200 ppm.