Biological control of cabbage root fly using an entomopathogenic fungus

Abstract: The aim of this study was to evaluate the effectiveness of the entomopathogenic fungus, Metarhizium brunneum as a biocontrol agent for the cabbage root fly Delia radicum. We investigated the ability of the fungus to infect below-ground larvae on radishes and Chinese cabbage as part of an integrated pest management (IPM) strategy.Radishes were grown in soil inoculated with the fungus M. brunneum as granular inoculum in a greenhouse environment. Two studies were performed. The first with experimentally added D. radicum eggs to all treatments, the second allowing for semi-natural oviposition within a net tunnel. Puparia were collected from the soil and incubated to hatch. From the second experiment, hatched flies were collected in three cages respective to treatment, Tween20, M. brunneum and untreated control. Unhatched puparia were dissected and plated on selective agar media to test for fungal infection for both greenhouse studies.In a field trial in Norway, Chinese cabbage were subjected to three treatments: M. brunneum-colonized rice incorporated in the soil at planting, Tween20 control on rice and an untreated control. Two weeks after planting, ten cabbage plants per plot were inoculated with seven D. radicum eggs to ensure a sufficient evenly distributed attack. Chinese cabbage heads, roots and surrounding soil were collected, after 60 days damage assessed and pupae isolated. Pupae will be analyzed in a similar manner to those collected from the greenhouse experiments; resulting flies will be placed in three cages according to treatment and egg laying compared, while unhatched pupae will be surface sterilized and plated on selective agar to assess fungal colonization.The interactions between M. brunneum, cabbage, and fly-larvae population analyzed in this study will be evaluated as a possible biological control application in an IPM context.