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Honey bee virus has evolved to become less deadly in a U.S. forest

Penn State researchers have made a significant discovery regarding the deformed wing virus (DWV) affecting honey bees. The team found that in at least one U.S. forest, the virus may have evolved into a less deadly form. This revelation offers hope for better management and treatment of the virus in bee colonies.

Less virulent strains 

The study compared deformed wing virus infection rates and severity in wild honey bees from a forest near Ithaca, New York, to those in managed apiaries in New York and Pennsylvania. The findings showed that while infection rates were similar, the virus genotype in wild bees resulted in milder infections than those in managed apiaries.

This suggests that similar to certain variants of human viruses leading to less severe infections, there could also be less virulent strains of DWV circulating among honey bee populations, explained Allyson Ray, a postdoctoral scholar at Vanderbilt University who led the study while she was a graduate student at Penn State. 

“Learning how different virus genotypes could result in more or less severe infections could help us better understand infection dynamics in managed bee colonies,” said Ray. “If we know certain variants have the potential to cause more harm, that could be helpful for bee care as well as improving our understanding of this virus’s epidemiology.”

Disease ecology theory

Christina Grozinger, a professor at Penn State and co-author of the study, said the work was an opportunity to examine virus dynamics in different types of bee colonies.

“Most research on honey bee-virus interactions focus on how bees respond to viruses and how we might be able to breed bees to become more resistant to the viruses,” said Professor Grozinger. 

“However, disease ecology theory predicts that in areas where viruses cannot spread as rapidly to new hosts, the viruses might evolve to be less damaging to their hosts, giving the viruses more time to spread to new hosts. We had a perfect opportunity to test this theory using the wild honey bees found in the Arnot Forest in New York.”

Varroa destructor mite

A major threat to honey bees is the Varroa destructor mite, which spreads the deformed wing virus. The infection causes various deformities in bees, most notably in their wings, which can render them unable to fly. This impairs the bees’ ability to forage and contribute to the hive.

The mite’s infestation can lead to significant colony damage, often killing bees and wiping out colonies within a few years without human intervention. Wild colonies without human care can be particularly vulnerable, noted the researchers.

The Arnot Forest

However, certain wild colonies, like those in the Arnot Forest monitored by Tom Seeley, a co-author of the study, have shown resilience to these threats. The researchers wanted to explore how these colonies managed to recover and bounce back from mite infestation.

“Previous studies found that the honey bees from the Arnot Forest still had mites and were not significantly more resistant to mites than bees from managed populations,” said Ray. “So, we hypothesized that rather than the bees being more resistant to the mites, the virus may have evolved to be less virulent and cause milder infections.”

How the research was conducted 

To investigate, the researchers collected bees from various locations across the Arnot Forest and in nearby apiaries in New York and in central Pennsylvania. The team analyzed infection rates across the three groups, extracted any virus present in the bees, and sequenced the virus genomes.

The results showed that there was no difference in the amount of virus present among the wild bees, and viral loads were also similar across groups.

Critical insights

Next, the researchers infected bees from two colonies in Pennsylvania with strains of the virus found in the Arnot Forest and the managed apiaries. The results showed that the Arnot Forest virus genotypes led to milder infections and better survival rates.

“At very low doses, we saw survival rates with this virus similar to controls,” said Ray. “This doesn’t make it an absolutely avirulent infection, but it does show that broadly, there are differences in infection based on the viral genotype the bees are infected with.”

The researchers said that in the future, more studies and assessments of the virus within the Arnot Forest could help them better understand the selection pressure that is leading to the virus’s evolution.

The research was supported by the United States Department of Agriculture (USDA) and National Science Foundation.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences

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