Insect Visitors of Black Cherry (Prunus serotina) (Rosales: Rosaceae) and Factors Affecting Viable Seed Production

Since 2000, wild black cherry (Prunus serotina Ehrh.) has produced erratic seed crops, especially in the Allegheny National Forest where poor seed production has been implicated in difficulties with black cherry regeneration in forest stands. Given that black cherry is insect pollinated and unable to produce viable seed from self-pollination, a reduction in seed crops could be due to a pollination deficit; however, its key pollinators are unknown. Identifying the pollinators and factors that influence pollinator abundance and fidelity is critical for supporting and enhancing seed production for this valuable timber species. Over a two-year period in developed, semideveloped, and forested areas in Pennsylvania, we identified the potential pollinators of black cherry and examined how their abundance, along with several other abiotic and biotic factors, influenced viable seed production. We found that andrenid (Andrenidae: Hymenoptera) bees are likely the most important pollinators. The proportion of viable seeds increased as the number of andrenids increased, and these ground nesting bees were most abundant on forest edges, highlighting this habitat's potential to support pollination services. Andrenids carried an average of 347-fold more black cherry pollen than flies and 18-fold more than halictid (Halictidae: Hymenoptera) bees. We did not find a significant relationship between the abundance of any other taxa besides andrenids and viable seed production. Black cherry flowers also provide resources for natural enemies such as the economically important parasitoid of Popillia japonica Newman (Scarabaeidae: Coleoptera), Tiphia vernalis Rohwer (Tiphiidae: Hymenoptera), which was observed feeding on black cherry nectar in this study.