The estimation of the dispersal rate of the adult cabbage root fly (Erioischia brassicae (Bouche)) in the presence of a brassica crop.
A marking method for Hylemya (Erioischia) brassicae (Bch.), in which the flies were fed on a sucrose solution containing radioactive phosphorus (32P) as the orthophosphate in hydrochloric acid neutralised with sodium hydroxide, was developed in investigations in central England. In dispersal experiments in 1968, marked flies were released in a 55 X 18-m plot of cabbage in a field of 1 ha. Recapture data were fitted to two empirical models relating the numbers of marked flies captured to the distance from the release point. The best fits were consistently obtained with a model of the form 1ny = a-b root x, where x is the distance from the release point, y is the number of flies caught there, a is a constant related to both the number of insects released and the position of the traps, and b describes the slope of the line. The average distances dispersed and rates of dispersal calculated from the model indicated that the wild population in a cabbage crop dispersed at a rate of 8-20 m/day. Recapture data obtained by previous investigators for Musca domestica L. [cf. RAE/B 41, 42] and Lucilia sericata (Mg.) [cf. 52,94] were re-analysed utilising the model for H. brassicae, and their rates of dispersal were found to be considerably greater than that of H. brassicae. This difference can be related to the flight behaviour of the three species. The observed relations between the numbers of flies recaptured and the distances from the release points are probably the result of the randomness and heterogeneity of movements compounded with an artefact introduced by the trapping procedures.