Laboratory tests with carabid ground beetles found in Wellesbourne fields indicated that intermediate-sized beetles such asBembidion tetracolum, Amara familiar is andAgonwn dorsale were more effective predators of cabbage root fly (Erioischia brassicae) eggs than small beetles, e.g.Bembidion lampros andTrechus quadristriatus, or large beetles, e.g.Harpalus rufipes andPterostichus melanarius. Further tests indicated thatA. dorsale would be an ideal predator, as it can survive up to one month without food, is not killed byP. melanarius, aggregates naturally, and eats large numbers of cabbage root fly eggs/larva.A. dorsale is also relatively easy to retain near the stems of plants by simple barriers and is not cannibalistic. Unfortunately, sufficientA. dorsale were not available for greenhouse trials. Greenhouse trials withB. tetracolum indicated that two beetles per plant were sufficient to control the high levels of cabbage root fly infestation normally encountered in the field at Wellesbourne.