SD27: Follow the pollen: The pollen budget of Cucurbita pepo and Xenoglossa pruinosa

Acorn squash (Cucurbita pepo) crops are entirely dependent upon insect pollinators for reproduction. In Ontario, Canada, their most important pollinator is the hoary squash bee (Xenoglossa pruinosa), a wild ground-nesting, solitary bee whose only source of pollen in the region is Cucurbita crops. As such, in this context, we have a unique opportunity to study the pollen budget of a cropping system in which a wild bee is the main pollinator. To evaluate the pollen budget in the acorn squash-hoary squash bee system, we measured pollen production by the crop, the pollen lost as “waste” due to the activities of hoary squash bees in staminate (male) flowers, pollen loads collected by female squash bees, and the number of pollen grains in fully provisioned hoary squash bee nest cells, comparing these to the crop’s pollination requirements as reported in the literature. From the perspective of both plant and bee reproduction, about 13% of the pollen produced by staminate acorn squash flowers was wasted, but it may be harvested by other organisms like ants. After accounting for waste, about 9% of the remaining pollen is needed for plant reproduction leaving the remaining 91% for hoary squash bee reproduction. We also evaluated the mass of pollen a female hoary squash bee could carry in a single foraging trip relative to her own body mass (~4%). This ecological information is useful for us to understand the relationship between a pollinator-dependent crop and an oligolectic wild bee species.