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 have the potential to influence the flowers that foragers visit, the pollen they pick up, and therefore the pollination service they provide to plants. In this study I present analyses of the pollen loads carried by individuals of the widespread generalized hawkmoth Hyles lineata (the white-lined sphinx moth). Proboscis pollen loads were collected from 390 wild moths caught at multiple sites using blacklights in the Santa Rita Mountains, Arizona. Pollen loads, collected and mounted onto slides, were counted and identified using an extensive reference collection of pollen from local flowering plants. We documented variability among individuals in the number and composition of pollen grains they carried, then examined the extent to which moth size and sex correlated with these patterns.
We report three key results. (1) H. lineata individuals vary extensively in the numbers of pollen grains and species carried: individuals carried between zero and 12 distinct pollen species, and between zero and several thousand pollen grains. (2) Female moths carried more pollen species and more pollen grains than males, and the relative proportions of different pollens within the loads differed between the sexes. (3) Surprisingly, smaller moths carried significantly more pollen species and grains than larger moths; size interacted with sex, such that small females carried more grains than small males. Together, these results suggest that individuals are likely to differ substantially in the pollen they deposit at the flowers they visit, and therefore are likely to differ in their effects on plant fitness. Variation in pollen loads reported here may be partially explained by foraging differences between male and female moths and between moths of different sizes, such as differences in activity patterns or floral preferences. 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.