As the reproductive success of many plants hinges upon animal pollen vectors, variation in floral visitation behaviors by these vectors has potential consequences for plant fitness. Previous work documenting how variation in visitor behavior translates into differences in plant reproduction has focused on comparisons among visitor species. Intraspecific variation in floral foragers has been frequently observed, however, driven by factors such as experience, body size, sex, and activity patterns. These differences can influence the flowers that foragers visit, the pollen they pick up, and therefore the pollination service they provide. To investigate how pollinators within species vary both within and between years and how pollinator traits affect foraging patterns, I analyzed the pollen loads of over 500 individuals of the widespread generalized hawkmoth Hyles lineata (the white-lined sphinx moth). Proboscis pollen loads were collected from wild moths at multiple sites using blacklights in the Santa Rita Mountains, Arizona across four years. Pollen loads were mounted onto slides, counted and identified using an extensive reference collection of pollen from local plants. We examined variability among individuals in the number and composition of pollen grains they carried, how moth size and sex influenced these patterns, and how these patterns varied between years.
We report three key results. (1) H. lineata individuals vary extensively in the numbers of pollen grains and species carried both within and between years. (2) Moth sex and size influenced pollen load composition, such that female moths carried more pollen grains than males, and the relative proportions of different pollens within the loads differed both between the sexes and between size classes. (3) The effects of sex and size varied substantially across time, with some pollen species consistently abundant on one group across years, while others shifted dramatically between sampling periods. These inter-annual differences were at least partially explained by shifts in both moth and plant phenology. Together, these results suggest that individuals are likely to differ substantially in the flowers they visit, and that both internal and external forces drive this variation. They also suggest that in some cases high intraspecific variation in pollinator behavior may exacerbate the consequences of phenological mismatching, due to mismatches between flowers and subsets of effective pollinators within visitor species. Ongoing work is investigating the behavioral differences that drive the observed pollen load variation, as well as how the differences in pollen load translate into reproductive consequences for flowering plants.