The Bioactivity of Beauveria bassiana and Isaria fumosorosea against the larval Stages of the Cowpea Beetle, Callosobruchus maculatus (F.)

Abstract

Abstract Entomopathogenic fungi, with their cosmopolitan existence and rich diversity, present a sustainable solution towards integrated pest management programs. Due to their eco-friendliness and bio-persistence, these entomopathogens are preferred to kill insects at various stages of their life cycle. The Cowpea seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), is an important bruchid pest in cowpea seed storages. The used pesticides against this pest have caused the occurrence of resistant populations and direct toxicity to the users. The objective of this study was to evaluate the mortality effects of two entomopathogenic fungi isolates obtained from fungi isolated from adults of C. maculatus collection, Beauveria bassiana and Isaria fumosorosea, against the larval stages of C. maculatus under laboratory conditions. The mortality percentage of 2nd instar larval mortality peaked at 100% when the B. bassiana spores’ concentration was 4*105. On the other hand, the effect of I. fumosorosea spores’ concentration on 2nd instar larvae peaked at 76.67% when the spores’ concentration was 4*105, while it peaked at 73.33% when the I. fumosorosea extract concentration was 100%. For 4th instar larvae, the results had shown the same pattern of effects by B. bassiana and I. fumosorosea spores and extract, with mortality percentage peaked at 96.67% when the B. bassiana spores’ concentration was 4*105, while it peaked at 83.33% when the B. bassiana extract concentration was 100%. In contrast, the effect of I. fumosorosea extract concentration on 4th instar larval mortality peaked at 70% when the extract concentration was 4*105, while it peaked at 73.33% when the I. fumosorosea extract concentration was 100%. For larvae, the relationship between the mortality percentage and (spores or extract) concentration, with increasing duration of exposure to the fungus spores, was positive, whereas the larval mortality increased when the fungus, spores or extract, concentration was raised.