A DNA-barcoding-based approach to quantitatively investigate larval food resources of cavity-nesting wasps from trap nests

Artificial nesting resources, also known as trap nests, have proven to be an ideal method for monitoring cavity-nesting bees and wasps, their collected food resources, and natural enemies. Nowadays, trap nests are frequently used to assess responses to environmental and biodiversity changes based on multi-trophic interaction networks. Here, we reconstructed quantitative trophic interaction networks of five apoid wasps (Trypoxylon clavicerum, Passaloecus corniger, Passaloecus gracilis, Psenulus fuscipennis, Isodontia mexicana and two vespid wasp species (Ancistrocerus nigricornis, Microdynerus parvulus) using DNA barcoding. Sampling the nests during their construction period allowed us to give an accurate count and identification of the provided food items. We recovered highly resolved bi- and tripartite networks including wasp-beetle larva, wasp-cricket, natural enemy-wasp-moth larva, natural enemy-wasp-spider, and natural enemy-wasp-aphid associations. The latter include aphid species that are known as agricultural and forest pests. Although the quantitative sampling of nests entails increased time costs, it enables not only high-quality DNA barcoding but also to reconstruct quantitative interaction networks. Thus, our approach is a highly promising monitoring tool for gaining deeper knowledge on the ecology, habitat requirements and the impact of environmental and biodiversity change on cavity-nesting bees and wasps.