Foliar damage, parasitoids and indirect competition: a test using herbivores of birch

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Abstract
The hypothesis that leaf‐chewing caterpillars and leaf miners indirectly compete via the influence of foliar damage on parasitoids was experimentally tested using the leaf miner Coleophora serratella (L.) and a complex of folivorous caterpillars on birch. Separate experiments tested the effects of manipulating artificial or caterpillar‐induced leaf damage on parasitism of leaf miners at several spatial scales. Parasitism of C. serratella by specialist and generalist parasitoids was independent of the extent of either collateral or leaf‐miner damage, whether experimentally or naturally induced. Support in the literature for the hypothesis is restricted to a single case, and only on a limited spatial scale; thus, the idea that collateral damage directs parasitoid‐mediated competition among herbivores remains highly speculative.