Intraspecific variation influences population and evolutionary dynamics as well as interspecific interactions. In plant-pollinator interactions, much attention has been paid to plant variation, but little to the pollinators themselves. In Lepidopterans, differences in nutritional requirements and flight behavior between males and females may lead to sex-specific foraging patterns. Here, we compare male and female foraging patterns of the rare, declining regal fritillary butterfly, Speyeria Idalia. First, we used a long-term dataset, which monitored the abundance, sex, and foraging of S. idalia along transects within Fort Indiantown Gap National Guard Training Center in Pennsylvania, USA, home to the last eastern S. idalia population. Then, in 2019, we captured male and female S. idalia in these same grasslands and swabbed them for pollen. We constructed a pollen library from all known nectar plants in bloom during capture and are identifying all pollen grains found on the butterflies to the lowest taxonomic level possible. We asked the following questions: (1) do females and males visit nectar plants at different frequencies;(2) do females visit a greater diversity of nectar plants; (3) which plant species contribute to any sex-specific foraging patterns; and (4) are foraging patterns similar across years?
Results/Conclusions
Based on all foraging observations in the long-term dataset pooled across years, we found that males and females visit nectar plants at significantly different frequencies. In fact, even when we removed the six nectar plants that contributed the most to the difference in frequencies between the sexes from the dataset, significant differences in foraging frequency remained. Females foraged on a greater number of species and significantly greater diversity of species, as measured by the Shannon diversity index, than males. These results were consistent across individual years for which we had robust sample sizes (N > 200). Because males emerge ~two weeks before females, sex-specific foraging patterns could be due solely to differences in nectar plant phenology. However, the patterns remain consistent when we restricted our analysis to the period of overlap in flight times between the S. idalia sexes. While pollen load processing is still ongoing, we have already identified >40 species visited by the butterflies that were not captured by the 20-year dataset, which was based on foraging sightings only. Clear sex-specific foraging in S. idalia has implications for understanding resource use in this rare species as well as pollination dynamics more broadly.