Dispersal of adult cabbage root fly (Erioischia brassicae (Bouche)) in relation to a brassica crop.
Adults of Hylemya (Erioischia) brassicae (Bch.) labelled with 32P were released 24 m from a plot of cabbage and recaptured with water traps. The responsiveness of the flies to the crop was observed, and average rates of dispersal were calculated [cf. RAE/A 61, 354]. Male and non-gravid females appeared to disperse mainly along hedges at random at average rates of 10-20 m/day, similar to flies released within or immediately adjacent to a brassica crop. The presence of the crop did not appear to influence movements or average dispersal rates. Gravid females flew upwind to the crop over distances of at least 24 m. This movement occurred at average rates of 80-40 m/day, at least three times as fast as the average rate of random dispersal of gravid females in the presence of a brassica crop. The behaviour of females in a 1 m cube cage in the proximity of the crop indicated that odour was probably a causative factor in the attraction of females. The odour of food-plants can thus act as an attractant as well as an aggregant in the food-finding behaviour of phytophagous insects. Gravid females responded to the crop by upwind flight, and it appears that attraction to food-plants is by way of anemotaxis stimulated by plant odour.