Different forms of mutural interference result in different spatial distributions of foraging Drosophila parasitoids Asobara citri and Asobara tabida

摘要

Females of the African sub-saharan larval parasitoid of Drosophila, Asobara citri, defend patches with hosts by fighting and chasing con-specific females it encounters. The palearctic, closely related species A. tabida does not defend patches and allows conspecific females to search in the same patch. The effect of patch defence by A. citri females searching simultaneously in a multi-patch environment on their distribution over these patches was investigated, and the distribution was compared with that of A. tabida. After having released the females at one spot the females of A. citri reached quickly a regular, ideal free distribution with a small variance compared to the mean number per patch, whereas the A. tabida females initially showed a high degree of clumping, followed by a gradual dispersion, and resulting in a more Poisson-like distribution over patches (variance-mean ratio closer to 1 than for A. citri). The latter might be caused by exploitation. Hypotheses about the adaptive significance of patch defence behaviour in the light of the natural history of both parasitoid species are briefly discussed.