Do host plants and gall tissue influence the composition of Diplolepis component communities?

Diplolepis rosaefolii and D. fusiformans induce simple galls on leaves and stems, respectively, of Rosa woodsii in western North America. Recent analysis suggests that these two gall inducers are synonymous and comprise a single species that also includes D. lens, which induces leaf galls on R. nutkana. All three taxa are also recorded from several other rose hosts, indicating that the species is flexible in both host and tissue affinities. We analyzed the component communities (parasitoids and inquilines) from galls of all three taxa and both host plants collected from a Palouse prairie remnant in southeastern Washington state. While the community members were largely the same, the relative abundance of some species notably varied between host galls. In particular, the torymid parasitoid Glyphomerus was largely absent from collections of D. fusiformans, while comprising over one-third of the component communities of D. rosaefolii. Similarly, the ichneumonid parasitoid Orthopelma was commonly reared from galls of D. lens, but only rarely from the other two taxa. If these three gall inducers in fact comprise a single species, differences in host tissue and host plant may be linked to variation in parasitoid pressure, a potentially important factor in natural selection within these communities.