Virulence of Beauveria bassiana ARP14 on two ladybird beetles: Harmonia axyridis and Chilocorus sp.

Abstract

Ladybird beetles are common predators that help reduce populations of many pest insects. In this study, we compared the virulence of a native entomopathogenic fungus, Beauveria bassiana ARP14, with a commercial strain (GHA) of the same species to two ladybird beetles, Harmonia axyridis and Chilocorus sp. The pathogen was applied via topical application in the laboratory at 1 × 10⁸ conidia/ml. The ST₅₀ values were not different between the ARP14 and GHA strains for larval H. axyridis, but were higher for the ARP14 strain for adults of both species. ARP14 showed less virulence against adult ladybird beetles than did GHA. However, the mycosis rates on larval H. axyridis by the ARP14 strain reached 83.3 % at 16 days after treatment, while it was 56.7 % for the GHA strain. Mycosis rates in adults were not different between the ARP14 (up to 56.7 %) and GHA (up to 43.3 %) strains. Chilocorus sp. adults showed higher mycosis rates in ARP14 (up to 80.0 %) than in GHA (up to 46.7 %) for the period from 15 to 20 days after treatment. Therefore, we conclude that B. bassiana ARP14 did not increase ladybird beetle’s mortality, its higher mycosis rate indicates a potential risk to beetles, requiring further study to assess ecological compatibility.