A Tale of Two Viruses
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By: Jay Evans
For mindless organisms with fewer than ten known proteins in their arsenal (several of which have the single role of building a shell to live in), bee viruses show a diversity of strategies to cause pain. As we learn more about the broad classes of honey bee viruses, it helps to understand what sets them apart. I will focus on two distinct viral groups, the paralytic ‘Aparaviruses’ and the Deformed wing viruses (DWV). They share two important traits: both are RNA viruses, and both are transmitted effectively by parasitic bee mites. The paralytic viruses include Acute bee paralysis virus (ABPV), Kashmir bee virus (KBV), and Israeli acute paralysis virus (IAPV) as a tight cluster of species with related proteins and impacts on bees. The DWV group is well studied and diverse, with two primary variants, DWV-A and DWV-B. DWV-A and DWV-B are kissing cousins and, in fact, recombinants between these strains are frequent and can be more damaging than their parents. Detailed studies of what unites and separates the paralytic and DWV groups help explain odd prior results and suggest different ways to battle each virus. After much work, a simplistic punchline for current research seems to be that 1) paralytic virus infection kills a high fraction of exposed bees quickly, while surviving bees do so by clearing out the infection through immune responses, and 2) DWV infection leads to copious virus growth in bees but most of these infected bees will survive to lead long, dumber, slower, and more ‘germy’ (infective) lives.
A key recent paper showing the interplay of these viruses was published by Vincent Prayugo and colleagues at the Universities of Illinois and Florida (Prayugo, V., Payne, A. N., Bonning, B. C., & Dolezal, A. G. (2026). Infection timelines and co-infection effects of Israeli acute paralysis virus and deformed wing virus in the honey bee (Apis mellifera). Journal of Invertebrate Pathology, 214, 108484. https://doi.org/https://doi.org/10.1016/j.jip.2025.108484). Using careful injections of young bees with a fine needle, they showed that the paralytic virus IAPV rose to high levels by one day into the experiment (it’s a little hard to know by how much the virus increased since there were no samples from the time of injection, but they had a LOT at day 1). That coincided with 30% of the bees dying the first day and steady high mortality up to ten days later. Oddly, IAPV was barely detected in surviving bees after day 1, even though bees continued to succumb to infection. A plausible explanation is that bees that could no longer maintain low virus levels were quickly swept into the dead pile. As someone who has chased a lot of ambulances trying to identify the causes of bee colony losses, mainly with a nose for viruses, this result echoes a frustration many of us share. Paralytic viruses are routinely implicated in bee colony losses by simply leaving their fingerprints….but they are generally poor quantitative predictors of colony death. Zachary Lamas, working with us at USDA-Beltsville and collaborators, built the case for this disconnect by showing suspiciously high levels of a different paralytic virus (ABPV) across apiaries in decline, but no difference in levels within dying versus healthy colonies or even in bees that were seemingly more sick than their sisters (Lamas, Z. S., Rinkevich, F., Garavito, A., Shaulis, A., Boncristiani, D., Hill, E., Chen, Y. P., & Evans, J. D. (2026). Viruses and vectors tied to honey bee colony losses. PLoS Pathogens, 22(2), e1013939. https://doi.org/10.1371/journal.ppat.1013939). Instead, the slow-growing, persistent DWV strains were the best indicator that death was nigh.
DWV is now the most-studied bee virus, according to Google Scholar, with nearly 10,000 entries; double that of sacbrood virus, which itself is followed by the paralytic viruses.
Much of the early work on DWV comes from the intriguing, but super rare, eponymous young bees with crumpled wings. Aided by genetics and the awareness that this virus was also causing lifestyle issues for normal-looking bees, research took off. A key discovery was that DWV infection was connected with cognitive issues, even for bees that looked fully fit (Iqbal, J., & Mueller, U. (2007). Virus infection causes specific learning deficits in honeybee foragers. Proceedings of the Royal Society B: Biological Sciences, 274(1617), 1517–1521. https://doi.org/10.1098/rspb.2007.0022). This led to studies showing that foraging bees infected with DWV were not bringing home the goods. Second, many studies found a link between DWV levels and poor colony outcomes, showing it to be a widespread predictor of colony loss.
What’s the good news from all this effort studying viruses? Bees seem to have genetically based traits that help reduce the impacts of bee viruses. In fact, mite-resistant lineages often survive the viruses carried by those mites (I reviewed some of these in the January 2023, Bee Culture essay: “Found in Translation: More signs of the resistance”). The mechanisms are still being worked out, but it often seems that selected bees persist despite viral infection levels that would kill others (the definition of tolerance). Tolerance is not a longterm solution (and indeed Nina Sokolov and colleagues argue persuasively that having hordes of germy but healthy bees flying around is not a solution at all: Sokolov, N. A., Boots, M., & Bartlett, L. J. (2025). Avoiding the tragedies of parasite tolerance in Darwinian beekeeping. Proceedings of the Royal Society B: Biological Sciences, 292(2040), 20242433. https://doi.org/10.1098/rspb.2024.2433). A real solution is to find bees, or medicines, that stop viruses in their tracks. Happily, many groups have their eyes set on just that.
These virus studies do not negate the fact that controlling virus sources in the hive (mainly mites but also sick nestmates, non-hygienic tools, surfaces, and stores) remains the best way to reduce virus impacts. Optimistically, parallel mite and virus breeding or management schemes seem to complement each other and, as such, can be additive in reducing bee losses. Letting bees battle both fronts in survivor-stock programs is one way to make progress, but so is nailing down the most important behavioral and immune traits for each and blending these into every breeding program. Tools for breeding hygienic bees are well established, and viral screens that ID stock with antiviral chops are becoming more available. Coupled with therapeutics, using these tools (or purchasing queens from breeders who do) should help you minimize a major source of colony loss. Whether your bees suffer from the Ebola-like flash of paralytic viruses or the dumb malaise of DWV, you can take steps now to help them survive, from mite control to healthy nutrition. With more complete record-keeping and better genetic tests, we could also find a time when the precise means of surviving or tolerating these threats can be addressed from queen to grave; stay tuned to science for that.
