Pollen dispersal in Cucurbita foetidissima (Cucurbitaceae) by bees of the genera Apis, Peponapis and Xenoglossa (Hymenoptera: Apidae, Anthophoridae)

Dispersal of buffalo gourd (Cucurbita foetidissima) pollen in Arizona at two sites and by two groups of pollinators is compared. Honey bees (Apis mellifera) were the primary pollen vectors in one cultivated field, and the squash bees Xenoglossa angustior, Peponapis timberlakei and P. pruinosa were floral visitors in another field. The foraging behavior of these bees is compared. Pollen admixed with fluorescent powders was used to indicate the distribution of pollen through each field. Statistical analysis of the distribution of flowers with marked pollen was made by the Kolmogorov-Smirnov two sample test and by logistic regression analysis. Although marked pollen was distributed farther by squash bees than by honey bees, the significantly different distribution of flowers on the vines in the two fields made analysis difficult. Squash bees dispersed marked pollen throughout the field and utilized all available pollen. Honey bees did not utilize all pollen but flowers and pollen dispersal were more uniform. Competition for pollen between honey bees and squash bees was reduced since the latter harvested most of the pollen standing crop before the honey bees became active. Both the native pollinators and honey bees in the absence of the other could effectively distribute pollen in their respective fields but honey bees could probably not compete as efficiently with native bees for pollen where the two groups occurred together.