Entomopathogenic fungi as potential biocontrol agents against Callosobruchus maculatus (F.) and Callosobruchus chinensis L. (Coleoptera: Chrisomelidae: Bruchinae) on stored cowpea seeds

Abstract

The insecticidal efficacy of four species of Trichoderma genius (T. harzianum, T. citrinoviride, T. viride and T. asperellum) and Metarhizium anisopliae was assessed against Callosobruchus maculatus and C. chinensis on cowpea seeds at concentrations of 2.0 × 106, 2.0 × 107, 2.0 × 108 and 2.0 × 109 conidia/kg. The adult mortality was counted 3 and 7 days after treatment while progeny and seed weight loss were recorded after 45 days. After 7 days, all fungal strains caused significant adult mortality of both insects particularly at 2.0 × 109 spores/kg. Metarhizium anisopliae and T. citrinoviride were the most effective fungi inducing 95 and 93.2% mortalities of C. chinensis at 2.0 × 109 spores/kg, respectively. Callosobruchus chinensis was slightly more susceptible to the fungal strains than C. maculatus. Furthermore, the fungal strains at the highest concentration caused a significant reduction in F1 progeny of both insects. After 45 days, T. harzianum at 2.0 × 109 spores/kg showed the highest protection of cowpea seeds against C. chinensis with weight loss of 6.5%. These findings indicate that the five fungal strains could be implemented in integrated pest management programs of these insects.