Beyond AFB: EFB, Chalkbrood, and Other Hive Health Threats

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title: "Beyond AFB: EFB, Chalkbrood, and Other Hive Health Threats" category: "Hive Health & Disease" summary: "American Foulbrood gets the most attention, but there are other diseases and pests that can stress or kill a colony. Here's how to identify EFB, chalkbrood, sacbrood, small hive beetles, and wax moths." readTime: 8 difficulty: "beginner" season: "year-round" slug: "efb-and-other-diseases" publishedAt: "2026-03-08" course: "beginner" module: "Hive Health & Disease" lessonOrder: 20

Most beekeeping disease discussions start and end with American Foulbrood. AFB is serious — it warrants its own article — but it's not the only disease threat your colonies face. European Foulbrood, chalkbrood, sacbrood, small hive beetles, and wax moths each have their own signatures, their own causes, and their own response requirements.

The good news is that most of these conditions respond well to management, and several resolve on their own with a strong colony behind them. The key is knowing what you're looking at so you don't confuse a manageable condition with something that requires immediate action.

European Foulbrood (EFB)

European Foulbrood is caused by the bacterium Melissococcus plutonius. Unlike AFB, which kills larvae after they're capped, EFB attacks young larvae in open cells, usually between 4 and 6 days old.

What it looks like:

• Larvae appear melted, twisted, or slumped in the bottom of the cell rather than in their normal C-shaped position
• Color ranges from yellow to brown — healthy larvae are pearly white
• Dead larvae dry into a rubbery, sometimes granular scale, but unlike AFB they are not ropy — a toothpick inserted into the cell won't pull a thread
• The smell is sour or vinegary — distinctly different from AFB's putrid, rotting odor
• Cappings may be perforated or removed by nurse bees attempting to clean out infected larvae

EFB is favored by conditions that stress young larvae: nutritional deficiency, cold snaps during buildup, or a high nurse-bee-to-larvae ratio imbalance. It's most common in spring, during rapid buildup, or after a foraging dearth.

What to do:

A strong colony experiencing a nectar flow will often clear a mild EFB infection on its own. Nurse bees have the hygienic capacity to remove dead larvae before the disease progresses. Management steps that help:

• Feed a pollen substitute if natural pollen is scarce — nutritional support improves larval survival and nurse bee hygienic behavior
• Requeen with hygienic stock if the infection recurs across multiple brood cycles
• Ensure the colony is populous enough to cover and warm all brood — chilled larvae are more susceptible

In the U.S., oxytetracycline is approved for EFB control. Unlike AFB, EFB does not form persistent spores, so treated equipment is not the long-term hazard that AFB equipment is. EFB is notifiable in some states — check with your state apiarist.

Chalkbrood

Chalkbrood is a fungal disease caused by Ascosphaera apis. It's one of the most visually distinctive brood conditions you'll encounter, and it's rarely fatal to a colony — but persistent infections are a sign that something in the hive environment needs to change.

What it looks like:

• Mummified larvae, usually white or chalk-colored at first, turning grey or black as the fungal spores mature
• "Mummies" are often found on the bottom board or at the hive entrance, where house bees have removed them
• Capped cells may be perforated or removed; you may find mummies still sitting in open cells if the infection is active

Conditions that favor chalkbrood:

• Poor ventilation — damp hive interiors are the primary driver
• Cold, wet spring weather
• Small colony that can't keep all brood warm
• Genetic susceptibility — some queen lines show poor hygienic behavior toward fungal infections

Management:

• Improve ventilation: screened bottom boards, remove entrance reducers once weather warms, verify the inner cover isn't trapping moisture
• Reduce to the number of hive bodies the colony can fully occupy — a large box on a small colony leaves cold, damp corners where fungus proliferates
• Requeen if infections persist through two or more brood cycles. Many beekeepers find that requeening eliminates chronic chalkbrood. Hygienic trait testing can help identify queens with better disease resistance.

There is no approved chemical treatment for chalkbrood. Management and requeening are the tools.

Sacbrood

Sacbrood is caused by Sacbrood virus (SBV), one of the most common bee viruses. It kills larvae shortly before or after capping, and the dead larva retains its skin in a distinctive fluid-filled sac shape.

What it looks like:

• Capped brood with sunken, darker cappings — similar to AFB at first glance
• When you remove the cap and carefully extract the larva, it appears as a fluid-filled sac with a darkened head
• The larva does not rope out on a toothpick — this distinguishes it from AFB
• The sac dries into a gondola-shaped scale that curls at the tip

Sacbrood is common in spring, particularly during the rapid brood expansion phase. It rarely reaches levels that threaten colony survival. Most colonies clear sacbrood virus on their own once the brood nest is strong enough to maintain high hygienic activity.

What to do:

In most cases — watch and wait. If sacbrood is present in scattered cells during spring buildup with no other symptoms, give the colony 2–3 inspection cycles before intervening. A thriving colony with strong nurse bee numbers will usually clear it.

If sacbrood persists extensively across multiple brood cycles, consider requeening — some queen lines show better resistance to SBV.

Small Hive Beetles

Small hive beetles (Aethina tumida, SHB) are an invasive pest from sub-Saharan Africa that have established in the southeastern U.S. and spread to parts of the Midwest, California, and internationally. They're a secondary pest — strong colonies defend against them effectively.

What to look for:

• Small, dark oval beetles (about 5mm) running from the light when you open the hive
• Larvae are white, 10–11mm, with rows of spines along their backs — they tunnel through comb, feeding on honey, pollen, and brood
• Heavily infested frames produce a fermenting, slimy mess that causes bees to abscond

Management:

• Keep strong colonies. Bees physically herd SHB into dark corners and coat them in propolis ("jail" behavior). A weak colony cannot maintain this defense.
• Beetle traps. AJ's Beetle Eater, Hood Traps, and similar in-hive oil traps are effective at reducing adult beetle populations when placed at the back of the bottom board.
• Control the ground under the hive. SHB pupate in soil. Plastic sheeting under hives or diatomaceous earth around hive stands reduces pupation success.
• Freeze drawn comb before storage — 24 hours at 0°F kills all beetle life stages. Never store unprotected drawn comb in a warm location.

SHB are primarily a risk in warm, humid climates. In the mid-Atlantic and further north, populations are limited by cold winters that kill overwintering adults.

Wax Moths

Two species of wax moths damage bee equipment: the greater wax moth (Galleria mellonella) and the lesser wax moth (Achroia grisella). Like SHB, they're a secondary pest — a healthy colony actively defends its comb. They become a real problem in stored equipment or in weak, compromised hives.

What to look for:

• Silky webbing and tunnels through comb
• White larvae (caterpillars) that are difficult to dislodge
• Burrowing damage to wooden frames — larvae sometimes bury themselves in the wood at the end of their tunnels
• "Bald brood" — patches of capped worker brood with the wax eaten away, exposing larval heads, caused by wax moth larvae tunneling beneath the cappings

Management in active hives:

• Keep colonies strong. Bees kill and eject wax moth larvae aggressively in a healthy hive.
• Reduce the hive to match the colony size — wax moths exploit unguarded corners of empty boxes.

Protecting stored equipment:

• Freeze all drawn comb before storage. 24 hours at 0°F kills all moth life stages.
• Store in a well-ventilated location. Air circulation discourages adult moths from laying.
• Para-dichlorobenzene (PDB) moth crystals — available as "No-Moth" crystals — can be used with stored comb. Use PDB specifically, not naphthalene (mothballs), which leaves residues toxic to bees. Air out treated comb thoroughly before returning it to the hive.

When to Act vs. When to Watch

| Condition | Immediate action needed? | |---|---| | EFB (mild, good colony) | Watch for 2–3 cycles; feed if nutrition is low | | EFB (recurring or spreading) | Requeen; consult state apiarist | | Chalkbrood (occasional mummies) | Improve ventilation; watch | | Chalkbrood (persistent) | Requeen | | Sacbrood (scattered cells) | Watch; usually self-resolves | | SHB (a few beetles) | Add traps; maintain colony strength | | SHB (larvae in frames) | Remove and freeze affected comb | | Wax moths (in hive) | Strengthen colony; reduce space | | Wax moths (in storage) | Freeze; use PDB; air out before use |

If you ever see suspected AFB — ropy pull, putrid smell, sunken dark cappings — stop the inspection and contact your state apiarist before touching any equipment from that hive. AFB requires a different response entirely.

Key Takeaways

• EFB affects young open larvae and smells sour — not the ropy, putrid sign of AFB. Mild cases often clear with a good nectar flow; persistent cases call for requeening.
• Chalkbrood mummies on the bottom board usually mean ventilation problems. Fix airflow first; requeen if it persists.
• Sacbrood in spring is common and usually self-resolving. Watch for two or three cycles before acting.
• Small hive beetles and wax moths are secondary pests — a strong, populous colony controls both. The real fix is colony strength, not traps alone.
• Always freeze drawn comb before storage. Twenty-four hours at 0°F eliminates SHB and wax moths at all life stages.