Insecticidal efficacy of two inert dusts and Trichoderma harzianum, applied alone or in combination, against Callosobruchus maculatus and Callosobruchus chinensis on stored cowpea seeds

The insecticidal effect of Trichoderma harzianum (TH), diatomaceous earth (DE), kaolin (KA) and their combinations against Callosobruchus maculatus (F.) and Callosobruchus chinensis L. (Coleoptera: Chrysomelidae: Bruchinae) was evaluated. The fungus T. harzianum was applied at 1 × 105, 1 × 106 and 1 × 107 spores/kg of cowpea seeds individually and mixed with 100, 500 and 1000 mg/kg of DE or KA. The effect of individual and binary treatments on adult mortality after 3 and 7 days of exposure was determined. The progeny production of both insects and weight loss in cowpea seeds were assessed after 45 days of exposure. Complete adult mortality of both insect species was achieved by using the highest application rate of DE/TH mixture (1000 mg/kg of DE+1.0 × 107 spores/kg of TH) after 7 days. A mixture of KA/TH (1000 mg/kg of KA+1.0 × 107 spores/kg of TH) caused 100.0 and 97.9% mortality of C. maculatus and C. chinensis, respectively, after 7 days of exposure. Progeny production of both insect species was significantly decreased for all individual and combination treatments compared to the control. No progeny of C. chinensis was detected in cowpea seeds treated with the mixture 1000 mg/kg of KA+‏ 1.0 × 107 spores/kg of TH after 45 days. Also, the combination treatments protected cowpea seeds from damage caused by C. maculatus and C. chinensis for 45 days. These results indicate that the combinations of TH fungus with DE or KA could be successfully used for the management of C. maculatus and C. chinensis in stored cowpea seeds. •The use of natural products is acceptable approach worldwide to overcome problems associated with synthetic insecticides.•Combination of T. harzianum with DE or KA gave satisfactory management of C. maculatus and C. chinensis on stored cowpea.•Complete adult mortality and progeny suppression were achieved by using high application rates of fungus with inert dusts.•The combinations of inert dusts and fungus were more toxic to C. chinensis than C. maculatus.