Efficacy of some combination insecticides against Epilachna beetle, Henosepilachna vigintioctopunctata (Fabricius)

The contact toxicity of three combination insecticides was determined against 10 d old grubs (mean wt. 0.02 g/grub) of H. vigintioctopunctata by atomization method under laboratory conditions (Temp. 28°C, R.H. 78%). At 48 HAE, deltamethrin + triazophos and profenofos + cypermethrin were equitoxic (LC₅₀ = 0.0003%) showing 1.5 times lesser toxicity than chlorpyriphos + cypermethrin (LC₅₀ = 0.0002%); and at 72 HAE, all the three were equitoxic (LC₅₀ = 0.0002%). In another experiment, the contact and stomach toxicity of six combination insecticides was determined against adults (mean wt. 0.021 g/adult) of H. vigintioctopunctata by leaf dip bioassay method under laboratory conditions (Temp. 28°C, R.H. 78%). At 24 HAF, beta-cyfluthrin + imidacloprid (LC₅₀ = 0.0001%) showed 130 and 9 times higher toxicity than ethion + cypermethrin (LC₅₀ = 0.0139) and chlorpyriphos + cypermethrin (LC₅₀ = 0.0009%), respectively; at 48 HAF, the order of toxicity was beta-cyfluthrin + imidacloprid (LC₅₀= 0.00004%) > chlorpyriphos + cypermethrin (LC₅₀= 0.0005%) > deltamethrin + triazophos (LC₅₀= 0.0009%) > ethion + cypermethrin (LC₅₀= 0.0024%) > profenofos + cypermethrin (LC= 0.0026%) > cypermethrin + indoxacarb (LC₅₀ = 0.0065%); and at 72 HAF, profenofos + cypermethrin and cypermethrin + indoxacarb proved equitoxic (LC₅₀= 0.0013%) being 65, 2.60 and 1.62 times less toxic than beta-cyfluthrin + imidacloprid (LC₅₀=0.00002%), deltamethrin + triazophos (LC₅₀= 0.0005) and ethion + cypermethrin (LC₅₀= 0.0008%), respectively.