Factors affecting the aggregation of the adult cabbage root fly (Erioischia brassicae (Bouche)) at hedges.
The effects of hedges and a lath barrier on the distribution of adults of Hylemya (Erioischia) brassicae (Bch.) in the field [cf. RAE/A60, 3692] was observed in central England with water-traps. Flies aggregated at the hedges and to a lesser extent at the barrier. The distributions of males and females were not correlated with the shelter effects of the windbreaks. This indicated that the flies did not aggregate by being carried passively on the wind and being 'held' in the turbulent air-flow to the leeward of windbreaks as suggested for other species [cf. 59, 1647]. Males and, to a lesser extent, females avoided shaded areas, and males were largely restricted in their movements to areas with vegetation. Adults of H. brassicae actively responded to several factors associated with the hedges and the barrier. They appeared to be attracted to the barrier probably by visual stimuli. Feeding sites such as hedgerow flowers probably acted as arrestants.