Honeybees Contribute to Bumble Bee Virus Prevalence

Honey bees might contribute to rising virus levels in wild bumble bees each spring, according to Penn State researchers who studied seasonal patterns of parasite and virus transmission in bees.

The study, published in the journal Ecosphere, revealed that honey bees consistently harbored higher virus levels than bumble bees. Moreover, while both bee species showed reduced virus prevalence in winter, only bumble bees had negligible levels by spring.

According to Heather Hines, corresponding author of the study and Associate Professor of Biology and Entomology in the College of Agricultural Sciences, this suggests that bumble bees that would not normally have a high virus prevalence each spring could be reinfected by honey bees.

The results, Heather Hines continued, contribute to the knowledge of the reasons behind the shifting pathogen populations in bees, their potential routes of transmission, and strategies for mitigating their effects.

Our data suggests that healthy wild bee communities require healthy honey bee colony management. Practices that help reduce disease loads in honey bees include ensuring cross-season high-quality nutrition, reducing pesticides, and mitigating Varroa mites, which are known to be responsible for higher late-season viral loads.”

Heather Hines, Study Corresponding Author and Associate Professor, Department of Biology and Entomology, College of Agricultural Sciences, Pennsylvania State University

Hines clarified that although the research identifies honey bees as springtime virus carriers, this does not imply that honey bees are inherently harmful, but rather that healthy pollinator communities depend on effective honey bee colony management.

Most wild plants and food crops in the world depend on pollinators to reproduce. While native bee species like bumble bees and solitary bees provide natural pollination services, can enhance fruitset - when a flower turns into fruit - and are essential for the pollination of many plant species, managed honey bee colonies are highly beneficial to agriculture as a pollination tool.

In contrast to honey bees, bumble bees are indigenous to the United States and serve as the primary ancestral pollinators for crops that are native to the area, including cranberries and blueberries. As they attract large numbers of new members to these resources, honey bees - which are native to Asia - are the best pollinators of the majority of orchard crops.

Although these various bee species share many characteristics, Hines pointed out that they also differ in ways that could impact dynamics such as the transmission of viruses and parasites.

Honey bees are managed bees that are perennial, while bumble bees are annual — overwintering as new queens and starting and growing their colonies in the following spring. These differing colony dynamics likely impact how diseases are spread between managed and native bees.”

Heather Hines, Study Corresponding Author and Associate Professor, Department of Biology and Entomology, College of Agricultural Sciences, Pennsylvania State University

Bee populations can be severely damaged by a wide range of pests and diseases, some of which can spread to affect different species of bees. For example, bumblebees and honey can contract diseases such as black queen cell virus (BQCV) and deformed wing virus (DWV). Bee populations can also become infected with dangerous parasites like parasitic flies and nematodes.

The purpose of this study was to investigate whether and how seasonal trends impacted the spread of viruses and parasites. They collected honey and bumble bees at six different locations in Center County over the course of four years.

The researchers then used molecular biomarkers to screen for DWV and BQCV in bee abdomens and used a microscope to screen for protozoan pathogens and parasites. Lastly, they contrasted how common these viruses and pests were in the various bee species at various points in the year.

Both bumble and honey bees were found to have common levels of DWV and BQCV, with higher levels of DWV in the fall and higher levels of BQCV in the mid-season. Nonetheless, honey bees consistently carried higher concentrations of both viruses.

According to Hines, the springtime seasonal variation was the most pronounced.

Bumble bees had negligible levels of viruses in the spring, suggesting queens are either resistant or die during overwintering if infected. Honey bee colonies tend to have lower viral prevalence by spring as well, however, they still retain fairly high viral levels compared to bumble bees. This means that honey bees serve as a viral reservoir that can reinfect native bee communities that would naturally purge these viruses in the spring.”

Heather Hines, Study Corresponding Author and Associate Professor, Department of Biology and Entomology, College of Agricultural Sciences

According to Hines, the study contributes to the increasing body of knowledge regarding the impact of managed honey bees on disease loads in bee communities.

To better understand which factors can be controlled to have the greatest influence on disease in these bees, the Hines Lab has specifically been involved in research examining the role of landscapes in the eastern United States on bumble bee pathogen loads.

Future research on pathogen susceptibility and queen immunity will, according to the researchers, enhance the comprehension of these patterns.