Dispersal and foraging behaviour ofPlatygaster californica: hosts can’t run, but they can hide

Abstract

Abstract1. Host–parasitoid models often identify foraging behaviour and dispersal distance as important for system persistence.2. Laboratory observations and field trials were used to characterise foraging behaviour and dispersal capability ofPlatygaster californicaAshmead (Platygasteridae), a parasitoid of the gall midgeRhopalomyia californicaFelt (Cecidomyiidae).3. Although foraging parasitoids meticulously searched plants in laboratory observations, none of the laboratory trials resulted in 100% parasitism, and the proportion of parasitism declined as midge egg density increased.4. The field trials showed that the distribution of parasitism over distance from a central release point was hump‐shaped, as predicted by a simple diffusion model. Mean parasitoid dispersal distance was 4.5 m, considerably farther than the 1.7 m mean midge dispersal found in previous work.5. Although the parasitoid appears to search thoroughly for midge eggs and to disperse farther than the midge, the results of this study show how this host–parasitoid system may persist due to spatially variable incomplete parasitism.