The United States is home to nearly 4,000 species of native bees, which play a fundamental role in pollination across agricultural, urban, and natural landscapes. In contrast, honey bees are not indigenous to this region, raising concerns that managed honey bee populations could harm wild bee species through competition for resources and the transmission of diseases, according to researchers from Penn State. However, their recent study indicates that among the 33 genera of native bees they examined, only a limited number appeared to be adversely affected by honey bee presence.
This comprehensive study, the largest of its kind, is currently available online and will be featured in the upcoming November issue of Science of The Total Environment.
The outcomes will assist in pinpointing bee groups that are potentially vulnerable and will support the development of conservation measures, as explained by Gabriela Quinlan, the primary author, and a postdoctoral research fellow at Penn State’s Center for Pollinator Research and College of Agricultural Sciences, supported by the U.S. National Science Foundation (NSF).
The research indicated that the existence of managed honey bee apiaries and urban land was associated with lower populations of six out of 33 wild bee genera, implying that these factors may hinder the ability of these bees to thrive. The study was conducted in areas where honey bee apiaries were denser in urban settings, prompting researchers to explore the impacts of apiary density compared to developed land.
Responses to these two factors varied across the six bee genera. The long-horned bees from the genus Svastra were most negatively impacted by apiary density, while the prevalence of another long-horned bee genus, Florilegus, was found to be most adversely affected by urbanization. Additionally, the impacted genera included green bees from Agapostemon and Augochlora, sweat bees from Lasioglossum, and long-horned bees from Melissodes.
Upon further data analysis, the researchers discovered that the bee genera most susceptible to apiary and land development tend to nest in the ground, forage later in the season, and, in some cases, specialize in certain types of flowering plants that bloom seasonally.
Quinlan noted, “Urban settings can pose significant difficulties for ground-nesting bees due to the presence of hard surfaces like asphalt and concrete, which restrict their ability to find bare soil for nesting.” She added that small bees are limited in their flight distance, making it challenging to locate nesting sites and flowers within their reach. Moreover, specialists need very specific types of flowers, which may be scarce in urban environments.
Some wild bees forage later in the season, coinciding with the peak population size of honey bee colonies, leading to increased competition for limited floral resources.
Quinlan suggested, “By planting late-season flowers and preserving areas of bare ground for nesting in urban gardens, we could help mitigate some of the challenges that urban development and beekeeping impose on these bee populations.”
The study involved collecting data on nearly 4,000 registered apiaries scattered across Maryland and mapping out their density within the state. This map was then compared against wild bee population data gathered by the U.S. Geological Survey’s Bee Monitoring and Identification Lab.
Researchers have noted that, in recent years, there has been a growing recognition of the decline in pollinator numbers attributed to factors like pesticides, pathogens, nutritional deficiencies, and climate change. Increased attention has also been directed towards the potential impacts of honey bees on wild, native bee populations through pathogen transmission and heightened competition for resources.
Despite these significant concerns, research detailing the effects of honey bee populations on wild bee numbers has been limited.
Christina Grozinger, a professor of Entomology, director of the Center for Pollinator Research, and a co-author of the study, stated, “Data on the population sizes of most wild bee species across the U.S. is quite scarce, leaving us with an incomplete understanding of the factors affecting various wild bee species.” She continued, “Our research specifically examined the link between managed honey bee populations and the reduction of wild bee abundance.”
Quinlan pointed out that their study offered further insights into how various bee genera, with different life histories, are influenced by environmental conditions.
For instance, they also observed that the density of apiaries negatively impacted the populations of the cuckoo bee Triepeolus, which preys on the nests of long-horned bees like Svastra. This suggests that diminished Svastra numbers could lead to a decline in Triepeolus populations. Grozinger emphasized the interconnectedness of these species, advocating for a perspective that views bees as communities rather than isolated species.
The researchers indicated that additional studies could be conducted in other parts of the U.S. to delve deeper into the specific responses of genera and species of wild bees to honey bees. Penn State’s new INSECT NET graduate training program aims to create nonlethal, automated monitoring technologies for bees and other insects to facilitate these investigations.
Grozinger also mentioned that one of the most effective ways for individuals to support both wild and managed bee populations is to incorporate more flowering plants into their surroundings, including urban areas and personal gardens.
“Particularly, native flowering trees and shrubs offer an abundance of resources for bees,” she explained. “By effectively managing pests and diseases within honey bee colonies, beekeepers can bolster their bees’ resilience to climate variations, which can also minimize the potential for honey bees to transmit diseases to wild bees.”
Individuals interested in learning more about available resources for bees in their regions and understanding the risks imposed by pesticides and environmental conditions can utilize the Beescape decision-support tool from Penn State.
Co-authors of this study include Jeffrey Doser from Michigan State University and Melanie Kammerer, a senior geospatial data scientist at EcoData Technology who earned her doctorate in Ecology from Penn State.
This research was supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture, Hatch Appropriations, and the NSF Postdoctoral Research Fellowship in Biology Program. For more insights on managed and wild bees and actions to assist bee populations, visit the Penn State Center for Pollinator Research website.
