COS 102-1 - Farmland diversification practices provide valuable resources for wild pollinator and predator communities but support an invasive insect pest

Abstract: Wild insect communities support agriculture through pest suppression and crop pollination, yet agricultural intensification and ecosystem simplification can have detrimental impacts on the abundance and diversity of beneficial insects. Farmland diversification could provide the resources that beneficial insects require, supporting insect biodiversity and ecosystem services. This idea stems from Root's 1973 Enemy Hypothesis, which posits that diverse plant communities provide diverse habitats and resources that cascade upwards, supporting a greater diversity and abundance of beneficial predatory and parasitic insects. Additionally, the establishment of functional plant species within agricultural areas can provide forage and nesting resources for wild pollinators, making these habitats a potential win-win for insect biodiversity and ecosystem services. Our team sampled six farmland diversification practices across 28 field sites in Delta, British Columbia, Canada. First, we evaluated insect diversity and abundance in three agricultural field types in and out of production (active crop fields in production, non-crop producing grassland set-asides and grassland set-asides with added flowers). Second, we assessed the community diversity of pests, predatory insects, and flower visitors across field margin types (planted hedgerows, remnant hedgerows, and unplanted weedy edges). Both set-aside practices (with and without added flowers) supported higher abundances and genus-level diversity of beneficial predatory ground beetles, and higher abundances of flower visitors than crop fields. Set-asides with added flowers supported higher beneficial insect abundance overall compared to traditional set-asides without flowers. In comparison, the overall intra-guild abundance and diversity of pests or natural enemies did not differ across field margin types. However, insects visited flowers in hedgerows more often than flowers in weedy margins. Despite the enhanced attractiveness of the hedgerows, the flower visitor community did not differ among margin types, suggesting that weedy margins also support flower visiting insects. We found a higher average abundance of Drosophila suzukii, a major invasive pest of berries, in both types of hedgerows compared to grassy margins and detected this pest in the fruit of many hedgerow species. This suggests that in some cases, farmland diversification may disproportionately support pest insects, particularly generalist invasive insects released from co-occurring natural enemies and competitors. Further work will consider the ability of newly introduced parasitoids of Drosophila suzukii to utilize these diversified habitats. These results provide evidence that farmland diversification can provide rich resources for wild insects, with potential positive and negative effects on surrounding crop production dependent on community composition and the successional dynamics of plant and insect communities.