Wax Moth in Stored Comb: What Actually Works

Every year the same thing happens, and almost nobody sees it happen. The supers come off in July or August, the frames go into a shed, and in October you open the stack to find grey silk, tunnels through the midrib, and a season's drawn comb reduced to a bag of webbing and frass.

The wax moth did not beat your bees. It got into comb your bees were no longer guarding.

Two moths, one problem

The greater wax moth (Galleria mellonella) is the destructive one; the lesser wax moth (Achroia grisella) does the same job more slowly. In both cases the adult moth is harmless — it has no functioning mouthparts and eats nothing. Everything that matters is done by the larvae.

And the larvae are not eating wax, exactly. They are after the protein: old cocoons, pollen, larval skins and brood residue left behind in the cells. This is why the damage is never evenly spread. Fresh drawn comb that has never held brood is a poor meal. Old, dark brood comb is a feast.

That single fact decides most of what follows.

Why storage is the dangerous part

Inside a working hive, wax moth is a non-event. Bees patrol the comb, find eggs and larvae, and throw them out. A strong colony simply does not have a wax moth problem, which is why the pest is often described as a symptom rather than a cause: moth damage in a live colony usually means the colony was already too weak to cover the comb it owned.

Take the frames out of the hive and every one of those defences goes with them. A stack of supers in a warm shed is undefended, unlit, unventilated protein — which is the exact description of ideal wax moth habitat.

The window in Sweden is short and specific. Larvae develop fast above roughly 20 °C, slowly between 10 and 20 °C, and essentially not at all below 10 °C. So the risk is concentrated in the weeks between the harvest and the first proper cold: August and September. Comb that survives to November survives the winter.

What actually works

Freezing — the reliable one.

Twenty-four to forty-eight hours at −18 °C kills every stage, eggs included. Eggs are the reason a shorter or warmer freeze is not enough; larvae and adults die easily, eggs do not. Freeze the frames, then store them somewhere a moth cannot reach them afterwards — sealed bags, or a stack closed top and bottom. Freezing is not a treatment that lasts; it is a reset, and re-infestation after it is entirely possible.

For most beekeepers with a chest freezer, this is the whole answer.

Cold, light and draught — the Nordic default.

Wax moth larvae dislike all three. The traditional storage method is a stack of supers criss-crossed at right angles so air moves through, in an unheated, light outbuilding. It costs nothing, and in a Swedish autumn it works, because the temperature does most of the job for you. What defeats it is a warm shed in August, or a sealed stack that holds warmth.

Bacillus thuringiensis aizawai — the one biological control with a registration.

B. thuringiensis is a soil bacterium that produces protein crystals toxic to certain insect larvae. The aizawai subspecies is specific to wax moth: a larva eats treated wax, the crystal activates in its gut, and it stops feeding and dies. Adult bees, brood and humans are unaffected, which is why it can be sprayed onto comb that will go back on a colony.

In Europe this is sold as B401 (Certan), by Vita Bee Health, as a registered product for wax moth control in stored comb. It is diluted with water and sprayed onto the comb before storage — it is preventive rather than curative, and applying it to comb that is already infested is largely wasted.

If you want a treatment for stored comb that is not simply cold, this is the one that has been through registration, and that is worth something.

Acetic acid (60–80 %) — the thorough, awkward option.

Fumigation in a sealed stack, with acid on absorbent pads between boxes. It kills eggs and larvae, and it has the useful side effect of killing nosema spores, which is why some beekeepers use it on comb from a colony that died. It is also corrosive: it attacks metal ends, frame nails and concrete floors, and it needs proper ventilation and gloves. Air the comb thoroughly before it goes near bees.

What to avoid

Paradichlorobenzene and naphthalene — mothballs. They work, and they are wrong. Both are fat-soluble, both accumulate in beeswax, and both carry over into honey. Neither is approved for use in hives in the EU. Comb treated with them is contaminated comb, and the contamination does not wash out.

The thing beekeepers underestimate

Wax moth is a comb problem before it is a moth problem.

Old brood comb is what the larvae are after, and it is also where disease spores and residues accumulate. A comb rotation — retiring the darkest frames every three years or so, and rendering them down for wax — removes the moth's food and the pathogen load in one move. Beekeepers who rotate comb rarely lose stacks to moth, and it is not luck.

Which is the honest summary of the whole subject: the moth is opportunistic, and everything you can do about it is really something you are doing about the comb.

The Swedish year, in order

July–August, at the harvest. Sort the frames as they come off. Anything dark and old goes to the wax melter now rather than into storage — you were not going to keep it anyway, and it is the frame the moth wants most.

Immediately after extraction. Let the bees clean the wet supers for a day or two, then treat and store. Wet comb left standing in warmth is the single most common way a stack is lost.

Into storage. Freeze if you can. Then cold, light and airy, criss-crossed, where you can see the stack.

October onwards. The cold is doing the work. Check the stack once, so that if something did get in you find it while it is still a few frames rather than all of them.

Nothing about this is difficult. It is almost entirely a matter of not leaving warm comb standing unattended in August.