Laboratory evaluation of the entomopathogenic fungus, Metarhizium anisopliae for the control of the groundnut bruchid, Caryedon serratus on groundnut

The pathogenicity of five isolates of Metarhizium anisopliae to adult Caryedon serratus was evaluated in the laboratory. All the isolates tested were virulent to the beetle but pathogenicity varied among the isolates. One isolate, CPD 4 was consistently superior to all other isolates in terms of mortality of the beetle, protection of groundnut pods from damage, reduction in progeny production and repellency to the beetle. At 10 days post-treatment, adult mortality treated with 0.1, 0.5 and 1.0 g of dry conidia equivalent to 3.6×10 8, 1.8×10 9 and 3.6×10 9 conidia of isolate CPD 4 per 50 g of groundnut pods was 100% which did not differ significantly from pirimiphos-methyl-treated pods at 10 ppm. At the lowest dosage of 0.1 g of conidia per 50 g of pods, damage in pods protected with isolate CPD 4 was 5% which did not differ significantly from the 2% damage in pods protected by pirimiphos-methyl at 10 ppm but significantly differed from damage in untreated pods which was 26%. Isolate CPD 4 caused complete reduction in progeny emergence at all dosages tested. It also exhibited some degree of repellency to the beetle with percentage repellency values of between 40–79% at concentrations of 0.1–1.0 g of conidia per 50 g of groundnut pods. These combined virulence and repellency characteristics of this isolate may increase its protectant potential against C. serratus.