Sub-lethal influences of different insecticides on oviposition preference of Helicoverpa armigera (Hbner) (Lepidoptera: Noctuidae) on cotton in relation to altered plant morphology

We investigated the sub-lethal influences of spinosad, chlorpyriphos, endosulfan, acephate and cypermethrin on the oviposition responses of Helicoverpa armigera (Hbner) to cotton plants, under cage and laboratory conditions. The rank order of toxicity (LC50 values as a per cent) of test insecticides against third instar larvae using the leaf disc method was: spinosadchlorpyriphos endosulfanacephate cypermethrin. On whole plants, females laid more eggs on acephate LC50-, acephate LC30- and cypermethrin LC50-treated cotton plants than on the control. The chlorpyriphos-treated plants were least preferred for oviposition. When excised cotton leaves from different treatments were used in a multiple-choice test, cypermethrin LC50- and endosulfan LC30-treated leaves received more eggs than the control. The repeated application of sub-lethal concentrations of different insecticides reduced plant height in the case of acephate LC30 and cypermethrin LC50, while plant spread and upper canopy leaf area were reduced in both treatments of acephate and cypermethrin. Reduced plant spread, upper canopy leaf area followed by plant height were found associated with oviposition preference by H. armigera females.