Adult solitary bees actively consume pollen throughout their life span

Background/Question/Methods

Bees depend on flowers for their sustenance, feeding mainly on nectar (as adults) and pollen mixed with nectar (as larvae); pollen is the principal component of larval food, but its consumption by adults is poorly understood. In social bees, adult worker females are known to eat pollen, whereas the importance of pollen feeding in the daily flower-visiting activity of solitary bees has not been established. Our aim was to determine the amount and frequency of pollen feeding by adult females and males of the solitary alkali bee, Nomia melanderi (Halictidae) foraging at alfalfa (Medicago sativa) near Touchet, Washington. Females (of different known ages) and males (at different times of the flight season) were collected at nesting sites at three different times of the day, killed by freezing, and dissected to remove their alimentary tract. Pollen contents in the crop, midgut and hindgut regions were qualitatively evaluated by visual scoring, and the number of pollen grains within full crops was quantified using hemocytometer methods.

Results/Conclusions

Both females and males proved to be regular and active consumers of pollen throughout their lifespan. Pollen feeding increased from morning hours, when flight activity started, to the late afternoon/early evening, when bees ceased flying, at which time most bees had crops that were full or nearly full of pollen. The number of pollen grains in full crops of females ranged from 30,000 to 50,000. These findings emphasize that the cost incurred by a flower’s male function in providing pollen as food to bee pollinators is not restricted to the collection of nest provisions, but also includes pollen eaten directly by adult bees as they visit flowers.