Honey Bee Health

Signs

When Varroa mite populations get out of hand, the effects ripple through your whole colony in ways that aren't always obvious at first glance. You might notice your bees seem weaker than usual, shorter-lived, and smaller in body size — that's the mites feeding directly on developing bees' fat body tissue, the organ that drives immune function, energy storage, and winter survival. As mite numbers climb, you'll often start seeing newly emerged bees with crumpled, shriveled, or missing wings and bloated, shortened abdomens — this is deformed wing virus being amplified and injected by the mites during development. Colonies with high mite loads also show general decline: fewer bees going into winter, poor foraging, and a population that just can't keep up. In heavy infestations, you may actually spot reddish-brown mites on adult bees or on white pupae when you open capped brood cells.

Treatment

Managing Varroa is an ongoing part of caring for a colony. Monitor regularly before choosing a treatment, and check again afterward to find out whether it worked.

An alcohol wash measures mites relative to the number of adult bees sampled. For example, six mites in a sample of 300 bees is a 2% infestation. A sticky board measures mites that fall over a period of time, usually expressed as mites per day. Its result is not an adult-bee infestation percentage, so the two numbers cannot be compared directly. Read the USDA alcohol-wash guide Read the USDA sticky-board guide

An action threshold is a monitoring result that calls for treatment. It depends on the sampling method, season, and colony conditions. Use current regional guidance rather than treating the example above as a universal treatment threshold. Oregon State University's Honey Bee Lab is a local resource for interpreting your results.

U.S. treatment options include oxalic acid, formic acid, thymol, amitraz, and hop-derived products. Choose a product registered for your state and follow its exact label, including temperature, colony-size, protective-equipment, and honey-super restrictions. Brood breaks and appropriate bee stock may also form part of a management plan.

Signs

Deformed wing virus is one of those pathogens where you often won't see obvious signs until a colony's Varroa problem has been building for a while. The most striking symptom is what gives the virus its name: newly emerged adult bees with wings that are crumpled, shriveled, or twisted instead of unfolding normally. These bees may also have bloated, shortened abdomens and look discolored compared to healthy workers. Because they can't fly, you may spot them crawling on the bottom board or in front of the hive. Beyond the obvious wing deformities, infected bees that look normal on the outside still suffer — their lifespan is shortened, their ability to learn floral routes is impaired, and they make poor foragers. A colony with escalating DWV pressure often shows a population that quietly collapses going into winter, even if things looked okay just a few months earlier.

Treatment

Varroa management is an important part of reducing DWV pressure because mites transmit the virus while feeding on bees. Use regular mite monitoring and the exact directions for any treatment you choose. A fall in the mite count does not, by itself, confirm that an affected colony has recovered. Work with an experienced bee-health adviser on the colony's condition and management rather than assuming that replacing the queen will reset a viral infection.

Signs

Black queen cell virus is tricky to spot because it largely hides in your worker bees without causing outward signs — but it reveals itself dramatically when it comes to queen rearing. If you're raising queens and find larvae or pupae that have turned yellow and then progressed to a dark brown or black color inside their cells, BQCV is the likely culprit. The blackening and decay of the queen cell wall itself is the classic field sign that gives the virus its name. In adult worker bees, the virus usually circulates without obvious symptoms. Some research has noted an association with K-wing, in which a bee's fore and hind wings are disjointed and held at a perpendicular angle, but this sign alone isn't definitive. For most colonies, BQCV is a background infection that only becomes a real problem when other stressors, particularly Nosema co-infection or heavy Varroa pressure, push viral activity into higher gear.

Treatment

There's no targeted antiviral treatment for BQCV, so the most effective approach is managing the conditions that allow it to escalate. Keeping your Varroa loads in check is foundational, since mite pressure weakens immune defenses across the board and Varroa-mediated co-infections amplify how damaging BQCV can become. Pay attention to Nosema as well — Nosema infections damage the gut lining in ways that allow BQCV to cross into the bloodstream and cause more widespread harm. Good sanitation practices, regular comb rotation, and requeening colonies that seem persistently unhealthy are all practical steps. If you're actively rearing queens and seeing high queen losses tied to BQCV, look carefully at your starter and cell-builder colonies for underlying health issues before assuming the problem is isolated to your queens.

Signs

Sacbrood shows up in your brood frames as an uneven, spotty pattern — the kind that makes you stop and look closer. Affected larvae die right around the time they would normally be capped, so you'll often find them in uncapped cells looking watery, discolored, or slumped out of the normal C-shape position. If you gently remove an infected larva, you'll notice it has a sac-like quality — the skin has toughened into a little pouch filled with fluid rather than completing its molt normally. Over time, these larvae dry down into a distinctive flattened shape that beekeepers often describe as resembling a canoe or gondola lying in the bottom of the cell. The color progresses from white through yellow to brown and eventually nearly black as the larva dries. One useful diagnostic detail: sacbrood-affected brood doesn't have the foul smell associated with bacterial foulbroods, which helps distinguish it in the field. The encouraging news is that sacbrood is one of the milder brood diseases — colonies with good hygienic genetics often clear it on their own.

Treatment

Sacbrood doesn't have a dedicated treatment, but most colonies with reasonable genetics will deal with it on their own over the course of a season. Your main job is to reduce the stress that's allowing it to persist. Check that your bees have access to adequate pollen and aren't dealing with a heavy Varroa load — both poor nutrition and high mite pressure compromise the immune responses bees use to detect and remove infected larvae. If sacbrood keeps coming back in the same colony across multiple seasons, that's a good signal to requeen with stock that has stronger hygienic behavior, since those bees will do a much better job of removing infected larvae before the virus can cycle further. Replacing old, heavily used comb can also help if reinfection seems to be a recurring pattern.

Signs

Lake Sinai Virus 2 is not a disease you'll diagnose by looking at your bees. There are no reliable visible field signs — no distinctive symptoms in the brood, no characteristic adult bee behavior, and no obvious decline you can attribute directly to this pathogen on its own. What research does show is that high viral loads have been associated with reduced colony performance and poorer overall health metrics. For practical beekeeping purposes, LSV2 is something you're more likely to encounter in the context of survey results and colony health research than something you'll identify in your own apiary without lab testing.

Treatment

Because LSV2 has no reliable field sign and no approved antiviral, management comes down to keeping your colonies as strong and stress-free as possible. The foundation of that is solid Varroa control, diverse and adequate nutrition, and avoiding management choices that unnecessarily weaken your bees. Colonies that are healthy and well-nourished are better equipped to carry viral loads without tipping into the kind of decline that threatens colony survival. If you participate in monitoring programs or have access to PCR testing through your state extension service, LSV2 screening can provide useful context when you're trying to understand unexpected colony losses.

Signs

Chronic bee paralysis virus produces some of the most striking and unusual-looking bees you'll encounter on an inspection. Affected bees show up in one of two ways: in the most visually dramatic presentation, adult bees look black, shiny, and hairless — almost like they've been rubbed smooth — and they tremble or shiver in a way that's distinctly abnormal. These bees often can't fly properly and you'll find them crawling on the ground outside the hive or clustered near the entrance. In a second, less common form, bees look bloated, hold their wings out at odd angles, and show similar trembling behavior. Both types tend to be rejected and bitten at the entrance by healthy hive-mates, so you may notice piles of these bees accumulating on the landing board or in the grass in front of the hive. Crowded colonies and those under stress seem more susceptible, which may help explain why it's seen more often in hobbyist yards than in commercial operations with more systematic management.

Treatment

Get help confirming the diagnosis and making a management plan for the affected colony. Other problems may be present at the same time and need their own diagnosis and care.

A 2020 report described two colonies with confirmed CBPV and additional health problems. One recovered after several management measures, including queen replacement and Varroa control; the other was lost after queen loss and weakening. This small case report cannot establish that requeening alone is the best treatment or predict a recovery deadline. Discuss the options with an experienced bee-health adviser rather than assuming the colony will recover within a set number of weeks. Read the CBPV case report

Signs

Nosema is one of the sneakiest pathogens in the hive because it rarely announces itself dramatically. Instead of obvious, easy-to-spot signs, you'll tend to notice your colonies quietly underperforming — they're not building up in spring the way you'd expect, queens are getting superseded more frequently than normal, and the overall population just seems to drag without a clear reason why. Individual infected bees live shorter lives and transition to foraging earlier than they should, which sounds subtle but adds up to significant productivity losses when you multiply it across thousands of workers. In more noticeable cases, you may see bees that appear disoriented or are wandering away from the hive unable to return. Because these symptoms overlap with many other conditions, a definitive Nosema diagnosis requires microscopic examination of bee guts to count spores, or PCR testing — it's worth sending a sample to a diagnostic lab or your state apiary inspector if you suspect it.

Treatment

Before treating for Nosema, confirm it with lab testing if at all possible — spore counts or PCR will tell you whether you're actually dealing with it and how severe the infection is. The most reliable thing you can do to reduce Nosema's impact is focus on the conditions that favor it. Keeping diverse, high-quality pollen sources available to your bees strengthens the midgut lining and overall immune response. Replacing old, dark comb removes a significant reservoir of Nosema spores that can reinfect bees season after season — this is one of the highest-return management steps for a Nosema-prone apiary. Maintaining young, vigorous queens keeps the colony's age structure young and resilient. Fumagillin has historically been the labeled U.S. treatment for Nosema, but its availability has been inconsistent in recent years and the research on its effectiveness specifically against Vairimorpha ceranae — the now-dominant species in western U.S. colonies — is mixed. Lean on the management practices above as your primary strategy, and treat medically only when you have a confirmed diagnosis and a legally available product in your state.

Signs

European foulbrood most often affects larvae before their cells are capped. Larvae may turn yellow, gray, or brown and lie twisted or slumped instead of forming a healthy, pearly-white C shape. The brood pattern may become patchy, and a sour smell can be present.

Capped brood can also be affected, sometimes with sunken or perforated cappings. These signs overlap with other brood problems, so open-cell damage or smell alone cannot confirm EFB or rule out American foulbrood. Ask for experienced help and confirmation before choosing treatment. Read OSU's European foulbrood interview

Treatment

Start with a confirmed diagnosis and advice from a veterinarian experienced with bees. In the United States, approved medically important bee antibiotics, including oxytetracycline, require veterinary oversight: a prescription or veterinary feed directive, depending on the product and how it is administered. Follow the veterinarian's directions, the exact product label, and any additional state requirements. Read the FDA's bee-antibiotic requirements

Colony nutrition, population, and management also matter. EFB can flare during stressful periods, including some pollination settings. Work with your veterinarian or extension adviser on a plan suited to the colony rather than assuming medication alone will resolve it.

Signs

Look for an irregular brood pattern, sunken or perforated cappings, brown larval remains with a ropy consistency, and dark scales adhering to the cell walls. An unpleasant smell may be present. A patchy brood pattern alone does not diagnose American foulbrood, and other brood problems can share some of these signs. Seek diagnostic help promptly rather than relying on appearance or smell alone.

Treatment

If you suspect American foulbrood, stop handling the affected colony and avoid transferring bees, honey, comb, or equipment to other hives. Arrange prompt diagnostic advice from a veterinarian experienced with bees and an appropriate bee-health adviser. Check the reporting and management requirements for your state before treating or disposing of material.

AFB spores can remain infectious for decades in contaminated material. Antibiotics may suppress active bacteria, but they do not kill the spores or make contaminated comb safe to reuse. A management plan may require destroying infected material or professionally decontaminating equipment; do not improvise a disposal or sterilization method. Read the FDA's American foulbrood overview

U.S. use of approved medically important bee antibiotics requires a licensed veterinarian's prescription or veterinary feed directive. Treatment must follow the exact product label and the veterinarian's directions. Read the FDA's veterinary requirements

Signs

Chalkbrood turns infected larvae into hard, chalk-like mummies. They may be visible in brood cells, on the bottom board, or at the entrance after workers remove them. Mummies can be white, gray, or black; dark coloration is associated with the fungus producing reproductive structures. Cool, damp conditions and colony stress can favor outbreaks, but the presence of chalkbrood does not identify a single cause.

Treatment

Management focuses on reducing conditions that favor the fungus and limiting its spread. Keep the colony well nourished, address excess moisture, and avoid transferring comb from an affected hive to another colony. Replacing old brood comb and considering a queen from resistant stock are management options; neither is a guaranteed cure. Hygienic behavior means workers quickly detect and remove affected brood. Ask an experienced bee-health adviser which steps fit your colony. Read the University of Florida chalkbrood guide