Coexistence of competing parasitoids on a patchily distributed host: Localvs. spatial mechanisms

I investigated mechanisms of parasitoid coexistence in a spatially structur ed host-multiparasitoid community (harlequin bugs [Murgantia histrionica] a nd two specialist parasitoids [Trissolcus murgantiae and Ooencyrtus johnson ii]), I tested both local and metapopulation hypotheses. The local hypothes is, intraguild predation, predicts coexistence if the inferior larval compe titor is superior at finding unparasitized hosts. Hence, the superior larva l competitor should be absent from patches of low host productivity. The me tapopulation hypothesis, dispersal-competition trade-off, predicts coexiste nce if the inferior competitor is a superior disperser. Hence, the superior larval competitor should be absent from patches isolated by distance. Mani pulative experiments demonstrate that coexistence does not require a disper sal advantage to the inferior larval competitor. Field surveys show that pa tches from which the superior larval competitor is absent are not the most isolated, but the least productive. In a natural experiment, loss of the su perior larval competitor was not associated with habitat loss or fragmentat ion that increases distance among occupied patches, but with a large reduct ion in host productivity. Taken together, these results strongly suggest th at 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. T he results have implications for multiparasitoid food webs in patchy enviro nments and offer practical insights regarding the release of multiple paras itoid species in pest control.