Plant-mediated indirect effects of carpenterworms on the insect communities attracted to fermented tree sap

Carpenterworm (Lepidoptera, Cossidae) larvae bore into trunks of the oak Quercus acutissima, thereby promoting sap exudation, and prey on insects attracted to tree sap. We examined the interactions between carpenterworms and sap-attracted insects to elucidate community-level consequences of carpenterworms and to estimate the relative magnitudes of their direct and indirect effects on community structure. Species richness, total abundance, and Simpson’s index of diversity (1/D) in tree sap communities were all significantly higher in carpenterworm-associated patches (sap-exuding patches that contained either larvae or larval nests) than in patches without evidence of carpenterworms. Abundance was also significantly higher in carpenterworm-associated patches for 10 out of 14 taxonomic groups, and this difference was much greater in the following groups that are sensitive to resource increases: drosophilid flies (Drosophilidae), sap beetles (Nitidulidae), and rove beetles (Staphylinidae). These results indicate that carpenterworms increase community size indirectly by increasing resource abundance, which is supported by the results of structural equation modeling (SEM). SEM also revealed that the direct effect of carpenterworms on species richness was weaker than their indirect effect, suggesting that predation by carpenterworms does not determine community structure. Similarly, carpenterworms can increase the abundance of some taxa by increasing resource abundance, and the predation pressure from carpenterworms on most taxa may be minor. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.