A snapshot in time: composition of native primary fauna of gall wasps in Spanish contact zones with chestnut trees infested by <i>Dryocosmus kuriphilus</i>

One of the most prominent problems related to biological invasions is the variation of local species composition, which often leads to <i>ex novo</i> interspecific interactions. Here, we explored and analysed the native species composition of gall inducers and their associated parasitoids and inquilines in Spanish areas invaded by <i>Dryocosmus kuriphilus</i> Yasumatsu 1951 (Hymenoptera: Cynipidae), an invasive pest of chestnut trees. After a quantitative description of these species' assemblages, we analysed through bipartite networks the level of the trophic specialisation of parasitoids and inquilines when considering either the host taxonomic identity, the host plant species or the host gall morphological type. We sampled galls of <i>D. kuriphilus</i> and native species of Cynipidae in different Spanish areas, including those where the exotic parasitoid <i>Torymus sinensis</i> Kamijo 1982 (Hymenoptera: Torymidae) had been released for <i>D. kuriphilus</i> biological control. The results indicate that the native parasitoids recruited by <i>D. kuriphilus</i> come almost exclusively from native communities on <i>Quercus</i> galls, except for one species from <i>Rosa</i>. Galls of <i>D. kuriphilus</i> had the second most diverse species composition; despite this species assemblage arose <i>ex novo</i> in less than a decade. The bipartite networks resulted more specialised when considering host plant taxa than when gall types and the host taxa were accounted. In such trophic webs, there were few parasitoid/inquiline specialist and many generalist species, which agrees with the rapid recruitment by <i>D. kuriphilus</i>. Higher parasitoid species richness in <i>D. kuriphilus</i> galls is likely due to their being a largely unexploited available resource for the native natural enemies of cynipid wasps.