Evaluation of the effectiveness of Metarhizium anisopliae on Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) and Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in laboratory

Abstract

Callosobruchus maculatus and Sitophilus zeamais are major storage insect pests of cowpea, Kersting's groundnut and maize in tropical Africa. These pests can cause post-harvest losses of up to 100% in a few months. The most common suppression method is the use of pesticides, with unfortunately important hazards and side effects. This study, evaluated the effectiveness of four isolates of Metarhizium anisopliae (ma351, ma356, ma357 and ma358) on C. maculatus and S. Zeamais in stored grains of cowpea, Kersting's groundnut and Maize, respectively. The pathogenicity of the four isolates was assessed and two of them (ma356, ma357) were the most effective. To study the virulence of these two isolates, four doses were used 0, 108, 109, 1010 conidia/100 grains. Results from the pathogenicity test indicated that all studied isolates were pathogenic to insects at a dose of 109 conidies/100 grains equivalent to 0.002 g/100 grains powder form. In the presence of isolates, the lifespan of treated pests was reduced compared to the control insect pests. The effectiveness of the isolates was significantly dose-dependent for all parameters evaluated except for imagos hatching rate of C. maculatus on cowpeas and seed weight loss in maize. The dose of 1010 conidia/100grains significantly reduced longevity of S. zeamais whereas with the dose of 109 conidia/100 grains reduction was already significant on C. maculatus for all parameters. This study built from experiments and speculated on how the production of entomophagenic fungi at large scale would be an alternative to the use of chemical pesticides in controlling population of C. maculatus and S. zemaïs in stored products and therein significantly reduce the overall post-harvest losses.