Bee Diseases & Pests
Varroa destructor gets most of the attention — and for good reason. But it is far from the only threat your colonies face. Bacterial infections, fungal diseases, internal parasites, and insect pests can all weaken or destroy a colony, often moving in when Varroa has already compromised bee health.
This guide covers every major disease and pest threat to honey bees beyond Varroa mites. For each one, you will learn how to identify it, what to do about it, and — most importantly — how to prevent it from gaining a foothold in the first place.
The Threat Landscape
Honey bees face a complex web of health threats that interact with and amplify each other. Varroa mites are the gateway — they suppress immune function, vector viruses, and create open wounds that admit secondary infections. But even in Varroa-controlled colonies, other pathogens and pests can cause significant losses.
| Category | Threats | Impact |
|---|---|---|
| Bacterial | American Foulbrood (AFB), European Foulbrood (EFB) | Brood death, colony collapse |
| Fungal | Chalkbrood, Stonebrood | Brood mortality, weakened colonies |
| Viral | DWV, Sacbrood, KBV, IAPV, CBPV | Shortened lifespan, deformities, paralysis |
| Protozoan | Nosema apis, Nosema ceranae | Dysentery, reduced lifespan, colony decline |
| Insect pests | Small Hive Beetle, Wax Moths | Comb destruction, honey fermentation |
| Mites | Tracheal mites, Tropilaelaps | Breathing impairment, brood damage |
💡 The best defense is a strong, well-nourished colony with low mite loads. Most secondary diseases gain a foothold only when colony health is already compromised.
American Foulbrood (AFB)
American Foulbrood is the most serious disease of honey bees. Caused by the bacterium Paenibacillus larvae, it kills developing bee larvae and produces spores that remain viable for 40+ years in equipment.
Identification
- Capped cells appear sunken, dark, and sometimes punctured
- Larvae die after being capped, turning from white to coffee-brown
- Ropiness test: Insert a toothpick into a suspect cell, stir, and slowly withdraw. AFB-infected material will string out 1-2 inches like hot cheese
- Scale: Dead larvae dry to a dark scale tightly glued to the lower cell wall that cannot be removed without breaking the cell
- Odor: Advanced cases have a distinct foul, protein-decomposition smell
The Rope Test — Step by Step
- Find a sunken, discolored, or punctured capped cell
- Insert a wooden toothpick or matchstick into the cell
- Stir the contents gently
- Slowly pull the toothpick straight out
- If the material strings out in a continuous rope 1 inch or longer, it is almost certainly AFB
⚠️ AFB is a notifiable disease in most jurisdictions. If you find it, you are legally required to report it to your state apiary inspector. Do not try to hide it or treat it quietly.
Management
There is no cure for AFB in contaminated equipment. Spores persist indefinitely.
- Burn: In many states, the protocol is to destroy the colony and burn all frames, comb, and bees. The hive body can be scorched with a torch if wooden.
- Shake: Some areas allow "shaking" — shaking bees off infected frames onto clean equipment and destroying all old comb. This carries risk of reinfection.
- Antibiotics: Oxytetracycline (Terramycin) can suppress symptoms but does not kill spores. Antibiotic use is now restricted and requires a veterinary prescription in the US.
Prevention
- Never buy used comb from unknown sources
- Sterilize tools between yards (fire or bleach solution)
- Replace comb on a 3-5 year rotation
- Inspect brood regularly — early detection is your only defense
European Foulbrood (EFB)
European Foulbrood is caused by Melissococcus plutonius. Unlike AFB, larvae typically die before being capped, making it easier to spot but also easier to miss if you are not looking carefully.
Identification
- Uncapped larvae appear yellowish, twisted, and melted in their cells
- Larvae are displaced from the normal coiled position
- Tracheal system may be visible as white tubes against yellow body
- No ropiness (unlike AFB) — dead larvae are watery or granular
- Odor is sour or acidic, not foul
Treatment
- Requeening is often effective — a break in brood cycle plus fresh genetics can allow the colony to recover
- Oxytetracycline (Terramycin) — requires veterinary prescription; used as a dust on brood frames
- Many cases resolve on their own when nectar flow resumes (improved nutrition helps bees fight the infection)
💡 EFB is often stress-related. Colonies with poor nutrition, heavy mite loads, or recent queen issues are most susceptible. Address the underlying stressors.
Chalkbrood
Chalkbrood is a fungal disease caused by Ascosphaera apis. It affects sealed brood, turning larvae into hard, chalk-like mummies.
Identification
- Mummified larvae — white, hard, chalk-like (later turning gray-black when fungal spores develop)
- Mummies are loose in cells — you may see them on the bottom board or at the hive entrance
- Sunken, punctured capped cells
- More common in cool, wet spring conditions
Management
Chalkbrood is generally a minor disease that resolves on its own as weather improves. Actions that help:
- Improve ventilation in the hive
- Requeen with hygienic stock (hygienic bees detect and remove chalkbrood quickly)
- Ensure adequate nutrition (protein supplement if pollen is scarce)
- Replace old comb that may harbor spores
- Avoid chilling the brood (do not open hives unnecessarily in cold weather)
⚠️ Chalkbrood is a symptom, not the disease. It usually means the colony is stressed by something else — poor nutrition, cold, mites, or a failing queen.
Sacbrood Virus
Sacbrood is caused by a virus (SBV) that affects developing larvae. It is one of the most common viral diseases but rarely causes significant colony decline on its own.
Identification
- Capped cells with punctured caps
- Dead larvae are sac-like — when removed with tweezers, they resemble a fluid-filled sac
- Color progresses from pale yellow to dark brown
- larvae are upright (not twisted like EFB) and have a pointed, gondola-shaped head
- Dry to a dark, brittle scale (easily removed from cell, unlike AFB)
Management
- Usually self-limiting — colonies recover as new bees replace infected brood
- Ensure colony is otherwise healthy (low mites, good nutrition)
- Requeen if the condition persists for multiple generations
- No chemical treatment exists — supportive care only
Nosema
Nosema is caused by two species of microsporidian parasites: Nosema apis (traditional) and Nosema ceranae (more recently detected, often more damaging). These parasites infect the midgut of adult bees, impairing digestion and shortening lifespan.
Identification
- Dysentery — brown streaks on the front of the hive, frames, or top bars
- Increased winter mortality or slow spring buildup
- Crawling bees at the hive entrance that cannot fly
- No visible symptoms in the brood — this is an adult bee disease
💡 Nosema cannot be diagnosed visually. Brown streaks suggest dysentery but could also be caused by bees being confined during cold weather. Definitive diagnosis requires microscopic examination of bee guts or PCR testing.
Diagnosis
- Collect 25-50 bees from the entrance (older foragers)
- Macerate abdomens in water
- Examine under 400x microscope for spores
- Or send samples to a diagnostic lab (many state extension services offer this)
Treatment & Prevention
| Approach | Details |
|---|---|
| Fumagilin-B | Antibiotic that suppresses Nosema — mix with fall syrup feed. Requires veterinary prescription in some areas. |
| Good nutrition | Strong pollen flow helps bees resist infection |
| Clean equipment | Replace old comb (spores accumulate in wax) |
| Ventilation | Reduce dampness in winter, which worsens dysentery |
| Comb rotation | Replace 2-3 frames per year to reduce spore load |
Small Hive Beetle (SHB)
The Small Hive Beetle (Aethina tumida) is a scavenger pest native to sub-Saharan Africa that has spread to the US, Australia, and parts of Europe. In strong colonies, bees can corral beetles into "prisons" and keep them under control. In weak colonies, beetles reproduce rapidly and can destroy a hive in weeks.
Lifecycle
- Adult beetles lay eggs in crevices near pollen and brood
- Eggs hatch in 2-4 days
- Larvae feed on pollen, honey, and brood for 10-14 days
- Larvae migrate out of the hive and pupate in soil (within 1 meter of entrance)
- Adults emerge in 3-4 weeks and seek new hives
Identification
- Adult beetles — dark brown to black, ~1/3 the size of a bee, quick-moving, hide in crevices
- Larvae — cream-colored, small, cluster in areas with pollen
- Fermenting honey — smells like rotting oranges, caused by beetle defecation in honey
- Slimy comb — larvae leave trails of slime across frames
Control Methods
| Method | How It Works | Effectiveness |
|---|---|---|
| Beetle blaster trap | Oil-filled trap between frames, beetles fall in | Good for monitoring and control |
| SWAT trap | Trap at top of hive with oil reservoir | Effective, fits under inner cover |
| Guardstar (permethrin) | Ground drench kills pupating larvae in soil | Reduces population over time |
| AJ's Beetle Eater | Small trap between frames, beetles enter through small holes | Inexpensive, effective |
| Hive strength | Strong colonies control beetles naturally | Best long-term defense |
⚠️ SHB thrives in warm, humid climates. Beekeepers in the Southeast US deal with SHB as a constant pressure. In northern states, it is mainly a concern in late summer and fall.
Wax Moths
Two species of wax moth attack honey bee colonies: the Greater Wax Moth (Galleria mellonella) and the Lesser Wax Moth (Achroia grisella). They are primarily a problem in stored equipment and weak colonies.
Lifecycle
- Adult moths enter hives at night and lay eggs in cracks and crevices
- Eggs hatch in 3-5 days
- Larvae tunnel through comb, eating wax, pollen, honey, and cocoon remnants
- Larvae spin silken tunnels through the comb as they feed
- After 4-6 weeks, larvae pupate inside the comb or on equipment
- Adults emerge in 1-2 weeks
Identification
- Silken webbing and tunnels through comb
- Larvae — white/cream, brown head, found tunneling in comb
- Damage — destroyed comb, frass (droppings), webbing
- Pupae — grayish cocoons in comb or attached to equipment
Prevention & Control
In stored equipment:
- Store drawn comb in freezing temperatures (< -12°C / 10°F) for 24+ hours to kill all stages
- Use Para-moth (paradichlorobenzene) crystals in stored supers — NOT mothballs (naphthalene is toxic)
- Store frames in well-ventilated, bright areas
- CO2 treatment in sealed rooms (if available)
In active colonies:
- Keep colonies strong — bees will chase out moth larvae
- Remove unused drawn comb from weak colonies
- Freeze frames before storing
💡 Wax moths are nature's cleanup crew. They are attracted to the protein-rich cocoon remnants left in brood comb. Freshly drawn comb with no brood history is far less attractive.
Tracheal Mites
Acarapis woodi are microscopic mites that live inside the breathing tubes (tracheae) of adult honey bees, primarily in the thoracic tracheae. They were a major pest in the 1980s and 1990s but have become less prominent with the rise of Varroa — though they are still present.
Identification
- Bees crawling at entrance with K-wing (wings held at odd angles, unhooked)
- Dyspnea — bees appear to be struggling to breathe
- Shortened lifespan, reduced foraging
- Large numbers of bees found dead at entrance in early spring
- Cannot be diagnosed without dissection — tracheae must be examined under microscope
Treatment
| Treatment | Method | Timing |
|---|---|---|
| Menthol crystals | Place 50g in mesh bag on top bars | Late fall or early spring, when temps are 15-27°C |
| Formic acid | Mite Away Quick Strips | Also controls Varroa — dual purpose |
| Grease patties | Sugar + vegetable oil patties on top bars | Prevention — discourage mite attachment |
| Vaporized oxalic acid | Standard Varroa treatment | Also effective against tracheal mites |
💡 Most beekeepers never see tracheal mites. They are controlled incidentally by Varroa treatments (especially formic acid). If you treat for Varroa, you are likely controlling tracheal mites too.
Integrated Pest Management (IPM)
The most effective approach to bee health is not reacting to individual diseases, but building a comprehensive management system that prevents problems rather than treating them.
The IPM Pyramid
- Prevention (base — always active): Strong genetics, good nutrition, clean equipment, regular inspections
- Cultural controls: Comb rotation, hive spacing, apiary site selection
- Mechanical controls: Screened bottom boards, trapping (SHB, moths), drone brood removal
- Biological controls: Hygienic breeding stock, beneficial microbes (not yet practical)
- Chemical controls (top — last resort): Targeted treatments only when monitoring thresholds are exceeded
Monitoring Calendar
| Month | What to Monitor | Method |
|---|---|---|
| February | Nosema signs, cluster health | Entrance inspection, heft test |
| March | Brood health, EFB, chalkbrood | Full inspection on warm day |
| April | Mite load (spring baseline) | Alcohol wash or sugar roll |
| May | SHB presence, queen performance | Standard inspections |
| June | Mite load, wax moth in stored equipment | Mite wash, inspect stored comb |
| July | SHB, mite load | Traps, mite wash |
| August | Mite load (critical fall window) | Alcohol wash — treat if >2% |
| September | Fall assessment, stores, EFB check | Full inspection |
| October | Final mite check, nosema prevention | Mite wash, fumagilin if needed |
| November | Winter prep verification | Heft test, entrance check |
Disease Prevention Best Practices
- Replace old comb — 3-5 frames per year. Contaminants and spores accumulate in wax over time.
- Practice apiary hygiene — sterilize hive tools between colonies (torch or bleach). Never share tools between apiaries without cleaning.
- Maintain genetic diversity — requeen from different genetic lines. Avoid having all colonies from the same breeder.
- Ensure adequate nutrition — protein (pollen) and carbohydrate (honey/syrup) stress makes every disease worse.
- Control Varroa — the single most impactful disease prevention step. Low mites = healthy immune systems.
- Avoid robbing — robber screens during dearths, do not leave honey exposed. Robbing spreads disease between colonies.
- Quantine new colonies — inspect purchased nucs and packages before placing them in your apiary.
- Keep records — track treatments, inspections, and outcomes. Patterns emerge over time.
When to Call Your Apiary Inspector
Contact your state or provincial apiary inspector if you:
- Find ropy brood (possible AFB)
- See unusual brood symptoms you cannot identify
- Experience sudden colony death (multiple colonies)
- Need guidance on treatment timing or options
- Are moving bees across state lines (inspection certificate required)
- Want to sell nucs or queens (inspection certificate required)
Most inspectors provide this service free of charge. They are a resource, not a threat. Building a relationship with your inspector makes you a better beekeeper.
Record-Keeping for Disease Management
Maintain a simple health log for each colony:
| Date | Colony ID | Inspection Findings | Mite Count | Treatment Applied | Notes |
|---|---|---|---|---|---|
| Apr 15 | Hive 3 | Good brood, SHB 2 adults | 1.5% | None | Queen laying well |
| Aug 20 | Hive 3 | Solid brood, low stores | 4.2% | Formic Pro | Feed 2:1 syrup |
💡 You cannot manage what you do not measure. A simple notebook or spreadsheet, updated after each inspection, will teach you more about your bees than any book or course.
References
[1] Shimanuki, H. & Knox, D. (2000). Diagnosis of Honey Bee Diseases. USDA Agricultural Handbook No. 690.
[2] Genersch, E. (2010). "Honey bee pathology: current threats to honey bees and beekeeping." Applied Microbiology and Biotechnology, 87(1), 87-97.
[3] Honey Bee Health Coalition. (2023). "Best Management Practices for Honey Bee Health." Managed Pollinator CAP.
[4] Neumann, P. & Elzen, P.J. (2004). "The biology of the small hive beetle (Aethina tumida)." Journal of Apicultural Research, 43(1), 9-21.
[5] Fries, I. (2010). "Nosema ceranae in European honey bees." Journal of Invertebrate Pathology, 103, S73-S79.
[6] Sammataro, D. & Avitabile, A. (2021). The Beekeeper's Handbook, 5th Edition. Cornell University Press.
[7] Caron, D.M. & Connor, L.J. (2013). Honey Bee Biology and Beekeeping. Wicwas Press.
[8] USDA Agricultural Research Service. (2023). "Bee Diseases and Pests: Identification Guide."