Response of insect pollinator guilds to winter heatwaves

Global climate change is causing more frequent extreme climate events. Unseasonable heatwaves are examples of extreme events that can disrupt biological processes when temperatures provide mismatched phenological cues to sensitive organisms. Heatwaves occurring in the winter may cause organisms to break dormancy prematurely and suffer from subsequent freezing events and lack of food resources. However, the effects of such events are poorly documented, including for pollinating insects, for which there is already concern over the possibility that climate change may decouple their phenologies with those of their host plants. To address this data gap, we deployed passive pollinator traps in central Oklahoma during four heatwave events in January and February to investigate which pollinators became active during times when no pollen and nectar were available.

All rounds of trapping collected pollinators, underscoring the impact of winter heatwaves on these flower-dependent insects. We found that trapping in the earliest portion of our study period collected primarily flies of several families, with bees and butterflies becoming increasingly common in later rounds. Unexpectedly, bees reputed to be the earliest-emerging species in the spring, such as members of genera Andrena, Colletes, and Osmia, were conspicuously absent. Instead, the majority of collected bees were females (presumably foundresses) of primarily eusocial halictid genera Lasioglossum and Halictus. If winter heatwaves disproportionately disadvantage certain pollinator taxa, such events may have downstream impacts on the composition of pollinator assemblages for the remainder of the growing season, and, by extension, the nature of pollination services rendered to the plant community.