Larvicidal toxicity of various insecticides against Tobacco caterpillar, Spodoptera litura, Fabricius (Lepidoptera: Noctuidae)

Abstract

The present study was envisaged to check the toxic effect of certain insecticides (chlorpyriphos, spinosad, novaluron, acetamiprid and thyme oil) on third instar larvae of Spodoptera litura by using three different bioassays i.e. topical treatment, leaf dip and artificial diet method at different concentrations viz., 5, 25,125 and 625 ppm. Observations on larval mortality were recorded from each treatment at 24, 48 and 72 hours intervals. Spinosad was found to be most toxic on the basis of larval mortality followed by chlorpyriphos, novaluron, thyme oil and acetamiprid in topical bioassay. But in leaf dip bioassay, thyme oil at 5 ppm caused 100 percent larval mortality. Acetamiprid proved as poor insecticide against this pest causing 26.66, 16.66 and 10 percent mortality after 72 hours of treatment in topical, leaf dip, and artificial diet bioassay at highest concentration, respectively. In artificial diet method, highest mortality percent was recorded in chlorpyriphos and spinosad i.e. 86.66 percent after 48 and 72 hours of treatment, respectively.