A review of the progress made to control the cabbage root fly (Delia radicum) using parasitoids

Some of the classical work on the effects of predatory ground beetles as pest control agents, was done at Wellesbourne in the late 1950s and early 1960s. Much of this work used the cabbage root fly (Delia radiculum) as the pest insect and the ground beetles species present in most cultivated fields in northern Europe as the controlling agents, Recent work, however, has shown that these ground beetles are not as effective as predators of the cabbage root fly as previously thought. In this paper, I will act as the Devil's advocate by questioning: (1) how many of these ground beetles can be considered to be truly ''beneficial''?, (2) how many can be relied upon to give predictable levels of control?, and (3) whether the methods now being proposed for enhancing the effects of such beetles are based on sound biological data? As the regulation of cabbage root fly populations by ground beetles now seems limited, I have now started to work on the two major parasitoids of this pest, one wasp (Trybliographa rapae) and one beetle (Aleochara bilineata) both of which can infest a relatively high proportion of the overwintering fly pupae. As this subject is new to me, I will use published data to describe my proposed approach. I hope the other participants can highlight the errors of my ways and indicate the lines of research they consider likely to prove most productive.