Effect of Repeated Sub-Lethal Applications of Different Insecticides on Egg Laying Preference by Helicoverpa Armigera(Hubner)on Cotton

摘要

The sub-lethal influences of repeated application of five insecticides viz,spinosad,chlorpyriphos,endosulfan,acephate and cypermethrin were determined on the egg laying preference of Helicoverpa armigera(Hubner)on different plant parts of cotton under caged conditions.The order of toxicity of test insecticides against 3rd instar larvae using leaf disc method was spinosad > chlorpyriphos > endosulfan > acephate > cypermethrin with LC_(50)values of 0.00004,0.00066,0.00804,0.06290 and 0.20870%,respectively.The application of acephate at LC_(30)(15.2 eggs)increased H.armigera oviposition on the upper surface of cotton leaves,while the plants treated with acephate at LC_(50)(25.0 eggs),spinosad at LC_(50)(13.4 eggs)and endosulfan at LC_(30)(14.3 eggs)received more eggs on lower surface of leaves than control(8.3 eggs).The egg laying on the fruiting bodies was higher in case of cypermethrin at LC_(50)(28.3 eggs)and acephate at LC_(50)(27.2 eggs)treatments than control(16.8 eggs).On whole plant basis,the females laid more eggs on acephate at LC_(50),(61.7 eggs),acephate at LC_(30)(42.2 eggs)and cypermethrin at LC_(50)(41.8 eggs)treated cotton plants than control(33.3 eggs).The chlorpyriphos treated plants were least selected for oviposition.The egg laying preference was clearly exhibited after repeated application(3 and 5)of insecticides as compared to single application.