PS 41-28 - Pollinator communities of the invasive tree, Pyrus calleryana in Northwest Ohio

Background/Question/Methods

Pyrus calleryana was intentionally introduced to North America from east Asia in the early 1900s as rootstock for the edible pear tree, P. communis. It was subsequently identified as an ideal urban tree, because of its small stature and profuse, early spring flowering. The characteristics that made the species good for agriculture and horticulture, including fire blight resistance and showy floral displays with small, inoffensive fruits, also allowed it to easily exploit novel ecosystems in its introduced range. The species has escaped cultivation and is typically found in open sites, including roadsides, prairies, and abandoned fields. In unmanaged sites, the species continues to proliferate, and the profuse flowering in early spring has the potential to alter pollinator species abundance and community diversity. The goal of this project is to characterize pollinator community diversity and compare it with expected pollinator diversity in Hancock County, Ohio. To characterize communities, pollinators were collected by hand and vacuum sampling on planted and escaped P. calleryana trees in April 2018 and 2020 and compared with species lists in published sources, including research-grade observations from iNaturalist.

Results/Conclusions

Eleven trees in Hancock County, Ohio were sampled once per season for fifteen minutes between noon and 4:00pm (EDT). Eight genera of pollinator were collected from P. calleryana flowers, with no detectable difference in species from planted and escaped trees. When compared with research-grade species lists derived from the Ohio Bee Atlas, an iNaturalist project administered by Ohio State University, seven of these genera were expected: Agapostemon, Apis, Bombus, Halictus, Lasioglossum, Megachile, and Xylocopa. Six additional genera were listed in the Ohio Bee Atlas, but not collected from P. calleryana: Andrena, Anthidium, Anthophora, Argochlora, Dialictus, and Hylaeus. The genus collected on P. calleryana, but not listed in the Ohio Bee Atlas was Osmia. P. calleryana hosts a broad community of pollinators, including both the commercially important pollinator Apis mellifera, as well as native, solitary pollinators of Osmia. Genera that were expected but not collected from P. calleryana include specialists unlikely to make use of P. calleryana, as well as species that are only marginally active when the tree is blooming. As populations of P. calleryana continue expanding northward, further study of its influence on pollinator populations and communities deserves attention, particularly in context of colony collapse disorder and climate change.