Dynamic Wasp and Sawfly Communities in Remnant Oregon White Oak (Quercus garryana) Fragments

Insects account for ∼64% of animal diversity and many groups, including wasps and sawflies, are poorly studied. Wasps and sawflies provide varied ecosystem services, but many species are declining, often because of land conversion, which can result in fragments of isolated habitat remnants surrounded by human-modified landscapes. There is a need to understand the conservation value of these remnants for insects. One such habitat in the Pacific Northwest, USA, is Oregon white oak (Quercus garryana) woodlands. To better understand the importance of oak fragments for wasps and sawflies, we sampled five fragments in The Dalles, Oregon, in the 2021 growing season. Our objectives were to examine: (1) seasonal trends in wasp and sawfly abundance and corresponding patterns in blooming flowers, (2) monthly relationships between small wasp and sawfly abundance versus bloom availability and land use, (3) seasonal variation in community composition of large wasp subfamilies, and (4) the relationship between seasonal variation and large wasp life history traits. We collected 18,852 specimens. Large and small wasp abundance was highest early and late in the season, while sawflies were only collected in May. Bloom availability declined seasonally, and temperatures peaked in July. In some months, small wasp and sawfly abundance was positively related to bloom abundance and negatively to surrounding agricultural land use. Large wasp community composition varied seasonally, as did their life history traits. This work demonstrates that remnant oak woodlands support abundant wasp and sawfly populations and a diverse large wasp community, which may contribute to biodiversity conservation and ecosystem services.