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

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 (Hübber) on different plant parts of cotton under caged conditions. The order of toxicity of test insecticides against 3^rd instar larvae using leaf disc method was spinosad > chlorpyriphos > endosulfan > acephate > cypermethrin with LC₅₀ values of 0.00004, 0.00066, 0.00804, 0.06290 and 0.20870%, respectively. The application of acephate at LC₃₀ (15.2 eggs) increased H. armigera oviposition on the upper surface ef cotton leaves, while the elants treated with acephate at LC₅₀ (25.0 eggs), spinosad at LC₅₀ (13.4 eggs) and endosulfan at LC₃₀ (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 LC₅₀ (28.3 eggs) and acephate at LC₅₀ (27.2 eggs) treatments than control (16.8 eggs). On whole plant basis, the females laid more eggs on acephate at LC₅₀ (61.7 eggs), acephate at LC₅₀ (42.2 eggs) and cypermethrin at LC₅₀ (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.