Collecting Flower Visitation Data
During each visit to the six farms, we took 30-min video recordings of pollinators visiting eight randomly selected male squash flowers per site (N = 112, mean video length: 30.87 min [sd: 3.75 min]). Each video was recorded between 07:30 AM and 12:00 PM on sunny, non-windy days. Video recordings were watched to record data on the identity and frequency of pollinator visitors to the flowers. Pollinators captured on video were identified to genus where possible (e.g., Apis ,Bombus , Eucera ), or to morphospecies for species that require close inspection and/or a key for accurate identification (Appendix S1: Table S2). Honeybees and bumblebees were easy to identify in the video recordings due to their relatively large body size and distinctive coloration. The behaviors of all other pollinators observed, including small green and olive halictids (e.g., Augochlora ,Augochlorella , Augochloropsis , Halictus , andLasioglossum genera), Melissodes spp., Eucera spp.,Triepeolus spp., Vespula wasp spp., and hover flies, were grouped together into an ‘other pollinators’ category to compare to honeybee and bumblebee behaviors in later analyses (see Statistics section).
During each individual pollinator’s visit to the observed flower, we recorded the duration (seconds) of each visitor’s interactions with specific flower parts, including petals (petal-only), nectar (nectar-only), pollen (pollen-only), and both pollen and nectar simultaneously (pollen+nectar). Typically, large-bodied bees, including honeybees and bumblebees, could not avoid contacting the stamen while drinking nectar (pollen+nectar) and led to relatively few observations of nectar-only interactions with flowers (Appendix 1: Table S3). For this reason, the nectar-only interactions were not considered as a substantial interaction type and were not included as a response variable in our main analyses. For each flower observed, the total duration of all types of interactions were summed for each pollinator group (honeybees, bumblebees, or all other pollinators) and then divided by the number of flower visits for the respective pollinator group to generate the duration spent per visit by each pollinator group to each flower. Finally, to test how each pollinator group’s visitation behavior impacted V. ceranae prevalence, we averaged the calculated visitation metrics for all flowers observed during the same site visit for each pollinator group. We followed the same process to calculate the average duration per visit of time spent on petal-only, pollen-only, and pollen+nectar interactions for each pollinator group. The number of visits for each pollinator group was the raw count of each type of pollinator that visited each observed flower within the 30-min observation period, which was then averaged for each of the two visits to each site.
Evaluating the average duration bees spent per floral visit ensured that the duration metrics accurately reflected the time bees spent interacting with flowers without being skewed by the number of bee visitors. Each additional bee visitor inherently increased the total duration of time bees spent on flowers (r = 0.76, t = 11.52, df = 95, p < 0.001) but did not necessarily increase the duration per visit time (r = 0.02, t = 0.21, df = 95, p = 0.84). We predicted that bees that spent a greater amount of time per visit interacting with flowers would have a greater likelihood of either depositing or picking up V. ceranae spores on flowers and would be correlated with higher V. ceranae prevalence.