Honey bees might be contributing to the rise of virus levels in wild bumble bees during the spring, according to a study by researchers at Penn State who examined how parasites and viruses are transmitted among bee populations.
Honey bees might be contributing to heightened virus levels in wild bumble bees during the spring, according to a study from Penn State that examined seasonal patterns of parasite and virus transmission in bees.
The research, published in the journal Ecosphere, revealed that honey bees typically carry higher virus levels compared to bumble bees. Moreover, while both types of bees showed a decline in virus prevalence during winter, only bumble bees had minimal virus presence by the spring season.
Heather Hines, an associate professor of biology and entomology in the College of Agricultural Sciences and the study’s corresponding author, noted that this indicates honey bees might be reintroducing viruses to bumble bees, which would otherwise have very low virus levels each spring.
She emphasized that these findings enhance the understanding of how diseases spread between wild and managed bee populations, as well as the reasons behind the fluctuation of pathogens in bees and potential measures to mitigate them.
“Our findings indicate that thriving wild bee communities rely on the proper management of honey bee colonies,” she explained. “Strategies to lower disease levels in honey bees should involve providing high-quality nutrition across all seasons, minimizing pesticide use, and addressing Varroa mites, known for elevating viral loads later in the season.”
Hines clarified that while the results suggest honey bees as reservoirs for viruses in the spring, it doesn’t imply honey bees are harmful; instead, effective management of honey bee colonies is crucial for maintaining healthy pollinator populations.
Globally, many food crops and wild plants depend on pollinators for reproduction. Managed honey bee colonies significantly aid agricultural pollination, whereas native bees like bumble bees and solitary bees offer essential natural pollination services, enhancing fruit set — the process of flowers developing into fruit — and are vital for pollinating numerous plant species.
Bumble bees are native to the U.S. and are the primary ancestral pollinators of local crops like blueberries and cranberries. In contrast, honey bees, originally from Asia, excel at pollinating orchard crops due to their ability to gather large groups quickly for pollination tasks.
Hines mentioned that while there are many similarities between these bee types, their differences impact how parasites and viruses spread.
“Honey bees are managed and perennial, whereas bumble bees are annual, hibernating as new queens and starting their colonies each spring,” she explained. “These differing colony lifestyles likely influence how diseases propagate between managed and native bees.”
A variety of pests and diseases can devastate bee populations, including some that can transfer between various bee species. For instance, deformed wing virus (DWV) and black queen cell virus (BQCV) can affect and spread among both honey and bumble bees. Furthermore, harmful parasites such as nematodes and parasitic flies can circulate among bee groups.
In their study, the researchers aimed to determine how seasonal changes influenced the spread of viruses and parasites. They collected both bumble and honey bees over several years at six different locations in Centre County.
Researchers then tested for DWV and BQCV in the bees’ abdomens using molecular biomarkers and identified protozoan pathogens and parasites with a microscope. Finally, they compared the presence of these viruses and pests in different bee species over time.
The analysis revealed that both DWV and BQCV were prevalent in honey and bumble bees, with higher DWV levels observed in the fall and mid-season spikes in BQCV for both species. However, honey bees consistently exhibited higher virus levels throughout the year.
Hines stated that the most significant seasonal variation was noted in spring.
“Bumble bees showed little to no virus presence in spring, indicating that queens are either resistant or perish during the winter if they are infected,” she noted. “Honey bee colonies also typically exhibit lower viral levels in spring, yet they still maintain significantly higher levels compared to bumble bees. Hence, honey bees act as viral reservoirs, potentially reinfecting native bee populations that would naturally eliminate these viruses in spring.”
Hines added that this study contributes to the growing body of research regarding the influence of managed honey bees on disease levels within bee communities. The Hines Lab has focused on examining how landscapes in the eastern U.S. affect bumble bee pathogen levels, aiming to identify manageable factors that could mitigate diseases in these bees.
Future research will investigate queen immunity and susceptibility to pathogens, providing further insights into these observed patterns.
Briana Wham, who earned her PhD in entomology from Penn State and now serves as a research data librarian at Penn State, is the first author of the paper. Co-authors include Elyse McCormick, a former research technician at Penn State now pursuing her doctorate at the University of Massachusetts; and several Penn State alumni who participated in the research as undergraduates, including Casey Carr, Nicole Bracci, Ashley Heimann, Timothy Egner, and M. Jesse Schneider.
This research was partially funded by a Northeast Sustainable Agriculture and Research Graduate Student Research Grant.
