Interpatch dispersal of the cabbage butterfly

The purpose of this project was to study the dispersal behaviour of female Pieris rapae (cabbage butterfly), with the goal of understanding the relationships between population abundance and dispersal mechanisms. Field studies indicated that (i) female flight orientation is not affected by the presence of a host plant patch, (ii) the number of eggs laid by a female on a patch is independent of patch size, at least within the range 18 to 18 000 plants, and (iii) dispersal rate of adult females from host plant patches is high. A model of egg abundance based on these assumptions was found to explain 85.4% of the variation in log egg abundance data taken from the literature. We suggest that, even though females disperse at high rates and are unable to orient towards host patches, populations maintain generally high abundances because host patches are common and widely distributed, and female flight paths are long. Both of these are expected to increase the probability of host detection.