Susceptibility of Epilachna varivestis Mulsant. (Coleoptera: Coccinellidae) to endemic isolates of Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae)

The Fungi Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) is widely distributed in nature and has the potential to control several important insect pest. We evaluated the susceptibility of Epilachna varivestis Mulsant. (Coleoptera: Coccinellidae) to four endemic isolates of B. bassiana derived from different insects and GHA strain of B. bassiana (Mycotrol® ES). For the bioassays, a group of 10 five days old adults were dipped in a fungal solution of 1 x 10⁸ conidia/ml in 0.01% Inex-A® surfactant. Adults were then transferred individually into sterile tubes and incubated in an environmental chamber at 25°C ± 2°C and 90% relative humidity. Mortality was recorded daily until 10 days post inoculation. Any beetle found dead was left in the tube and was examined daily for visual signs of mycosis. Each treatment was replicated seven times using different batches of conidia. Control specimens were treated with 0.01% Inex-A® surfactant. Epilachna varivestis adults were susceptible to B. bassiana, although the infection rate was different among isolates. Mean separation revealed that the highest mortality of 71% and 51% was observed using endemic isolates Bb37 and Bb40 derived from Melanoplus differentialis and Phyllophaga sp. at 10 days after inoculation, respectively, while mortality in the GHA treatment (11%) was not different from endemic isolates Bb38 (39%) and Bb41 (37%) derived from Phyllophaga sp., and wireworm (Elateridae), respectively. The activity of E. varivestis adults decreased sharply from three days after inoculation. The results are discussed with respect to the potential for biological control of E. varivestis using B. bassiana.