Physiological condition of adult cabbage root fly (Erioischia brassicae (Bouche)) attracted to host-plants.
Abstract
The author has found that the stages in the ovarian cycle of female of Hylemya (Erioischia) brassicae (Bch.) can be numbered in a similar way to that of other Muscids [cf. RAE/A 60, 37] and the stages are described. Oviposition could be identified by the presence of an expanded ovarian sheath or the presence of corpora lutea. Mating was identified by the presence of sperm in the spermathecae. These criteria were used to assign females to physiological classes. When adults labelled with 32P were released at a hedge 19.5 m from a cabbage plot and recaptured in water traps, only nulliparous mated females in the final stage V (gravid) moved upwind to the crop, dispersing during an initial 2-h period at an average rate of 95 m/day and subsequently at 35 m/day. Females of other classes and males dispersed into a cereal crop in all directions within the trapping area, showing no tendency to move upwind. The dispersal rates were about 50 m/day in the later periods of the experiments, 2-3 times higher than previously observed. The cereal crop appeared to reduce or eliminate the association of H. brassicae with hedges and increased the dispersal rate in comparison with that noted when flies dispersed in one dimension (along the hedge).