Honey bees spread viruses to bumblebees in the spring 

Honey bees may play a significant role in increasing virus levels in wild bumblebees each spring, according to a study conducted by researchers at the Pennsylvania State University. 

By analyzing seasonal trends in the transmission of parasites and viruses among bees, the experts found that honey bees consistently carried higher levels of viruses compared to bumblebees. 

Additionally, while both bee species showed lower virus prevalence during the winter, only bumblebees experienced negligible virus levels by spring.

Honey bees may reinfect bumblebees in spring

Heather Hines, an associate professor of biology and entomology at Penn State’s College of Agricultural Sciences and the study’s corresponding author, suggested that these results indicate honey bees might be reinfecting bumblebees in the spring, a time when bumblebees would otherwise have very low virus prevalence.

“Our data suggests that healthy wild bee communities require healthy honey bee colony management,” Hines said. 

“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.” 

Importance of honey bee colony management 

According to Hines, while the study highlights honey bees as spring viral reservoirs, this does not imply that honey bees are detrimental. Rather, it underscores the importance of good honey bee colony management for the overall health of pollinator communities.

Pollinators are vital for the reproduction of many food crops and wild plants worldwide. Managed honey bee colonies significantly benefit agriculture by pollinating plants, while native bee species like bumblebees and solitary bees provide natural pollination services that can enhance fruit set and are essential for many plant species. 

Dynamics of parasite and virus spread

Bumblebees, native to the United States, are particularly important for pollinating crops like blueberries and cranberries, while honey bees, originally from Asia, excel in pollinating most orchard crops due to their ability to recruit large numbers of foragers.

Hines argued that although honey bees and bumblebees share many traits, they also have differences that influence the dynamics of parasite and virus spread. 

“Honey bees are managed bees that are perennial, while bumblebees are annual – overwintering as new queens and starting and growing their colonies in the following spring,” she explained. These differing colony dynamics likely impact how diseases are transmitted between managed and native bees.

Bee viruses across seasons

The study focused on the spread of viruses and parasites across seasons, particularly examining deformed wing virus (DWV) and black queen cell virus (BQCV), which are harmful to both honey and bumblebees and can spread between species. 

The researchers collected both types of bees at multiple time points across four years from six sites in Center County. They then screened the bees for viruses using molecular biomarkers and for protozoan pathogens and parasites using a microscope, comparing virus and pest prevalence across different seasons.

The results showed that both DWV and BQCV were common in honey and bumblebees, with DWV levels peaking in the fall and BQCV in mid-season. 

However, honey bees consistently harbored higher levels of these viruses throughout the year. The most significant seasonal difference was observed in the spring.

Honey bees as a viral reservoir 

“Bumblebees had negligible levels of viruses in the spring, suggesting queens are either resistant or die during overwintering if infected,” Hines said. 

“Honey bee colonies tend to have lower viral prevalence by spring as well; however, they still retain fairly high viral levels compared to bumblebees. 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.”

Broader implications of the study 

The study contributes to the growing body of research on the impact of managed honey bees on disease levels in bee communities. 

The Hines Lab has been particularly involved in exploring how landscapes in the eastern United States affect bumblebee pathogen loads, aiming to identify manageable factors that can most effectively reduce disease in these bees.

Looking forward, the researchers plan to conduct further studies on queen immunity and vulnerability to pathogens, which could provide deeper insights into these patterns and help inform strategies for bee conservation.

The study is published in the journal Ecosphere.

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