Coexistence of Competing Parasitoids on a Patchily Distributed Host: Local vs. Spatial Mechanisms

I investigated mechanisms of parasitoid coexistence in a spatially structured host–multiparasitoid community (harlequin bugs [Murgantia histrionica] and two specialist parasitoids [Trissolcus murgantiae and Ooencyrtus johnsonii ]). I tested both local and metapopulation hypotheses. The local hypothesis, intraguild predation, predicts coexistence if the inferior larval competitor is superior at finding unparasitized hosts. Hence, the superior larval competitor should be absent from patches of low host productivity. The metapopulation hypothesis, dispersal–competition trade-off, predicts coexistence if the inferior competitor is a superior disperser. Hence, the superior larval competitor should be absent from patches isolated by distance. Manipulative experiments demonstrate that coexistence does not require a dispersal advantage to the inferior larval competitor. Field surveys show that patches from which the superior larval competitor is absent are not the most isolated, but the least productive. In a natural experiment, loss of the superior larval competitor was not associated with habitat loss or fragmentation that increases distance among occupied patches, but with a large reduction in host productivity. Taken together, these results strongly suggest that parasitoid coexistence occurs via local interactions rather than spatial processes. This study provides the first empirical evidence of the role of spatiotemporal variation in host productivity on parasitoid coexistence. The results have implications for multiparasitoid food webs in patchy environments and offer practical insights regarding the release of multiple parasitoid species in pest control.