Influence of some New Insecticides Mixtures against Cotton Bollworms and Their Side Effects on Associated Predators

Bollworms resistance to most registered insecticides has become a major obstacle to their successful chemical control with conventional insecticides. Therefore, field experiments were conducted at Sakha Agricultural Research Station in 2010 and 2011 cotton seasons to study the efficiency of four new mixtures (M) of insecticides, i.e. chloropyrifos + cypermethrin (M1), chloropyrifos + lufenuron (M2), flufenoxuron + alpha-cypermethrin (M3) and thiamethoxam + lambda-cyhalothrin (M4) and two conventional insecticides, chloropyrifos and alphacypermethrin, against cotton bollworms, Pectinophora gossypiella (Saund.) and Earias insulana (Boisd.). Also, their side effects on associated predators were studied. In 2010 season, M3 and alpha-cypermethrin in three successive sprays of each proved to be the superior recording 81.58 and 79.85% reduction in larval infestation, respectively. M4, M1 and chloropyrifos came in the second order without significant differences causing 77.38, 76.65 and 75.27% reduction, respectively. M2 was the least effective with reduction percentage of 74.15. The results of 2011 season showed the same trend of effect for all the tested compounds. According to their side-effects against associated predators, the tested toxicants could be arranged descendingly as follows, alpha-cypermethrin (81.00), M4 (77.96), M3 (76.68), M1 (69.02), M2 (66.07) and chloropyrifos (64.28) % reduction. The obtained results indicated that, the new tested mixtures of insecticides did not exhibit additional advantages in control of the cotton bollworms comparing to the conventional toxicants, where they showed approximately the same effectiveness against the pest and were harmful to  the associated predators. Moreover, cross-resistance could be developed after repeated application of these mixtures.