Pollen collection from returning foragers
Pollen pellets were collected from individual bees as they returned from a foraging bout at each of the three sites, and over five time periods (Table 1). Within each time period we aimed to collect pollen from 40 honey bee and 20 bumble bee individuals on each of three days at each site, moving among sites each day to randomize data collection. Individual bees were immobilized in a cooler with ice, both pollen pellets removed, and each pellet separately stored in 1.5 mL microcentrifuge tube labeled with bee species, site, period, bee number, and pellet (a) or (b). Upon return to the laboratory, the pollen pellets were placed in a -20oC freezer until ready for drying and weighing. One pollen pellet per bee was dried at 45oC for 24 hours, then used to identify plant morphotypes present in pollen loads.