by A recent study conducted by Penn State researchers has found that the deadly deformed wing virus (DWV) in bees may have evolved to be less deadly in at least one forest in the United States. This discovery has potential implications for preventing or treating the virus in managed colonies.
The study, which was published in the Proceedings of the Royal Society B, compared the rates and severity of DWV in wild honey bees from a forest near Ithaca, New York, to bees from managed apiaries in New York and Pennsylvania. While infection rates were similar across all groups, the researchers discovered that a particular virus genotype found in the wild honey bee population caused milder infections than the virus found in the managed apiaries.
This finding suggests that, similar to certain variants of human viruses that result in less severe infections, there may also be less virulent strains of DWV circulating among honey bee populations. Allyson Ray, a postdoctoral scholar at Vanderbilt University who led the study while a graduate student at Penn State, explained that this discovery could be helpful in monitoring and caring for bees in the future.
Understanding how different virus genotypes can result in more or less severe infections is crucial in comprehending infection dynamics in managed bee colonies. Ray stated, “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.”
The study provided an opportunity to examine virus dynamics in different types of bee colonies, according to Christina Grozinger, the Director of the Center for Pollinator Research at Penn State. Most research on honey bee-virus interactions focuses on how bees respond to viruses and how to breed bees that are more resistant to them. However, disease ecology theory suggests that in areas where viruses cannot spread rapidly to new hosts, they might evolve to be less damaging to their hosts, allowing them more time to spread. The wild honey bee population found in the Arnot Forest in New York provided the perfect opportunity to test this theory.
The researchers highlighted that DWV and the Varroa destructor mite, which spreads the virus, are two of the biggest disease threats for honey bees. Infestations of mites can cause significant damage to colonies by living and feeding on bees directly, as well as by spreading DWV. The virus is most harmful when it infects bee pupae, leading to deformations and high mortality rates upon reaching adulthood.
Managed colonies can be completely wiped out by mite infestation and associated viral infections within a few years without proper intervention. Wild colonies, which do not receive human care, are particularly vulnerable. Nevertheless, some colonies worldwide have managed to recover and bounce back from mite infestation, including those in the Arnot Forest. The researchers sought to determine the factors contributing to these bees’ better outcomes in combating mites and DWV.
Previous studies showed that honey bees from the Arnot Forest still had mites and were not significantly more resistant to them than bees from managed populations, suggesting that the virus may have evolved to be less virulent and cause milder infections. In managed apiaries, honey bee colonies are often placed close together, leading to increased transmission of viruses among colonies. In contrast, wild bee colonies in the Arnot Forest are spread farther apart, reducing the opportunities for bees to come in contact and spread the virus.
To investigate the resilience of Arnot Forest bees to disease, the researchers collected honey bees from various sites across the forest, as well as from nearby apiaries in New York and Pennsylvania. They analyzed infection rates among the three groups and sequenced the virus genomes. Bees from two colonies in central Pennsylvania were also experimentally infected with virus strains from the Arnot Forest and the managed colonies for comparison.
The researchers found that the amount of virus present was similar in wild bees and managed bees in both New York and Pennsylvania, with infection rates ranging from 40% to 57% across the three groups. However, when comparing the survival rates of Pennsylvania bees infected with different virus strains, they discovered that the virus genotypes from the Arnot Forest caused milder infections and better survival compared to the viruses from the managed colonies.
At low doses, the survival rates with the Arnot Forest virus strain were similar to the control group. Although it is not an absolutely avirulent infection, the study shows that there are differences in infection based on the viral genotype. Further research within the Arnot Forest will help scientists understand the selection pressure influencing the evolution of the virus.
This research was supported by the United States Department of Agriculture (USDA) and the National Science Foundation. Allyson Ray was awarded the 2023 Penn State Alumni Association Dissertation Award for her work on this study and was supported by a USDA Predoctoral Fellowship.
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