Data from: Omnivory in bees: elevated trophic positions among all major bee families

As pollen- and nectar-foragers, bees have long been considered strictly
herbivorous. Their pollen-provisions, however, are host to abundant
microbial communities, which feed on the pollen before/while it is
consumed by bee larvae. In the process, microbes convert pollen into a
complex of plant and microbial components. Since microbes are analogous to
metazoan consumers within trophic hierarchies, the pollen-eating microbes
are, functionally, herbivores. When bee larvae consume a microbe-rich
pollen complex, they ingest proteins from plant and microbial sources,
thus should register as omnivores on the trophic “ladder.” We tested this
hypothesis by examining the isotopic compositions of amino acids extracted
from native bees collected in North America over multiple years. We
measured bee trophic position across the six major bee families. Our
findings indicate that bee trophic identity was consistently and
significantly higher than that of strict herbivores, providing the first
evidence that omnivory is ubiquitous among bee fauna. Such omnivory
suggests that pollen-borne microbes represent an important protein source
for larval bees, which introduces new questions as to the link between
floral fungicide residues and bee development.