Biological control of the cabbage root fly (Delia radicum) using an entomopathogenic fungus (Metarhizium brunneum)

Cabbage root flies are a damaging pest to cruciferous crops in the northern hemisphere. They are considered to be the main pest of brassica crops (EPPO, 2004). Their larvae feed on the roots and stems of brassica plants. Larval feeding causes quality reductions in crops like turnips, rutabaga and radishes, as well as stress to important crops like broccoli and cauliflower. Insecticide use is limited, and there are few alternative management strategies. Alternative options include using physical barriers like nets covering the crop or vertical net fences to block flies entering the enclosed area, using plant volatiles and trap cropping to lure cabbage root flies away from important crops, and using natural enemies to reduce cabbage root fly populations. Biological control agents including entomopathogenic fungi, like Metarhizium brunneum, can be considered a part of integrated pest management for cabbage root flies. In this study two greenhouse experiments, and a field study were performed to assess the ability of M. brunneum, isolate Met. 250/O2, to reduce cabbage root fly populations by lethally infecting cabbage root fly larvae and pupae. The influence of M. brunneum inoculation of plant roots on how the female adult cabbage root fly lays her eggs was tested, as well as the egg-laying ability of surviving flies collected from Met. 250/O2 inoculated treatments. However, no significant effect of Met. 250/O2 was found; Met. 250/O2 treatments did not reduce pupae survival or reduce the number of cabbage root fly larvae and pupae samples collected or influence how many eggs adult female flies laid. However, M. brunneum should still be considered a part of integrated pest management for cabbage root fly populations, with further research.M-P