Efficacy of three microbial insecticides alone or in combination with diatomaceous earth for the control of Callosobruchus maculatus

Abstract

The management potential of three microbial insecticides, spinetoram (SP), emamectin benzoate (EB) and ivermectin (IV), at the application rates of 0.25, 0.5 and 1.0 ppm and diatomaceous earth (DE) at the application rates of 100, 500 and 1000 ppm and their binary mixtures was tested against Callosobruchus maculatus (F.) on cowpea seeds. The effects of all individual and combined treatments on adult mortality (after 3 and 7 days of treatment), F₁ progeny (after 45 days), and weight loss in cowpea seeds (after 45 days) were evaluated under laboratory condition. The results showed that the binary combinations at the lower tested concentrations of three tested microbial insecticides (SP, EB and IV) and DE caused a total adult mortality (100.0 %) of C. maculatus after 7 days of exposure. It was also clear that the tested microbial insecticides in combination with DE were more effective against C. maculatus than the materials alone. No progeny of C. maculatus was produced at the highest concentrations of a mixture of DE (1000 ppm) + IV (0.5 ppm) after 45 days of treatment. Moreover, all combinations of tested microbial insecticides and DE decreased or suppressed the damage caused by C. maculatus on cowpea seeds and gave a complete protection of seeds for 45 days of treatment without negative effects on seed germination. These findings indicate that combinations of microbial insecticides with inert dust could be a useful approach for the effective management of C. maculatus on stored cowpea seeds.