Further experiments on the effect of beetle predators on the numbers of the cabbage root fly, Erioischia brassicae (Bouché), attacking brassica crops

SUMMARY Further experiments to determine the importance of beetle predators were carried out at Wellesbourne during the three years 1960‐62. By using barriers to restrict the movement of adult carabids into and out of plots of brassica crops it was shown that the survival of the immature stages of the root fly was inversely related to the population level of predatory carabids. After excluding adult carabids almost entirely from the plots it was estimated that they had been responsible for up to one‐third of the total egg mortality, although this varied with the species composition of the carabid population. Initial differences in egg survival resulting from predation by carabids were reduced as the cabbage root fly life‐cycle progressed and were due to other losses of which predation by adult Staphylinidae was important. Such differences in egg survival, however, led to substantial crop yield reductions, particularly in dry weather.