With recent declines of some pollinators, including native bees, many land managers are implementing restoration and conservation plans to enhance native bee habitat. However, information is limited about which plant species serve as major food sources for native bees. Current methods for identifying food sources for bees (e.g., behavioral observation, light microscopy) only document a snapshot of bee foraging behavior and often require specialized expertise. DNA metabarcoding provides an opportunity to avoid these pitfalls and potentially reveal a more detailed record of bee foraging behavior. The objectives of this study are to 1) determine major food sources for native bees in three study locations, and 2) compare pollinator networks derived from behavioral observations vs. DNA metabarcoding data. In summer 2018, we sampled 589 native bees from three locations in eastern Oregon. We documented foraging behavior by recording the flower species that each bee was visiting when sampled. We washed all pollen from each bee, extracted DNA from pollen mixtures, and used DNA metabarcoding to identify the plant species in each pollen mixture.
Results/Conclusions
Bees were recorded visiting over 50 species of plants, with 60% of all bee visits occurring on just 10 plant species. Most commonly visited plants included both native species (e.g., shaggy fleabane (Erigeron pumilus), slender cinquefoil (Potentilla gracilis), mountain monardella (Monardella odoratissima), Missouri goldenrod (Solidago missouriensis), whitestem frasera (Frasera ablicaulis), and hoary tansyaster (Machaeranthera canescens)), and non-native species (e.g., diffuse knapweed (Centaurea diffusa), yellow star-thistle (Centaurea solstitialis), bull thistle (Cirsium vulgare), and tumblemustard (Sisymbrium altissimum)). Plant-pollinator networks created from DNA metabarcoding data were more complex than those created from behavioral observations, indicating that metabarcoding provides a more complete record of bee foraging behavior relative to behavioral observations. This study suggests that metabarcoding pollen collected from foraging bees may be an effective way to create more accurate and reliable lists of attractive plants for conservation and restoration efforts to benefit native bees.