Impacts of the Greater & Lesser Wax Moths on Honey Bee Colonies
Another common pest of honey bee hives are the two wax moth species: the greater wax moth, Galleria mellonella and the lesser wax moth, Achroia grisella. It is the larvae, not the adult moths that threaten bees. Wax moth larvae tunnel through wooden frames to consume the comb underneath, producing a trail of silken webs that can destroy weaker colonies.
The most straightforward method of controlling wax moths is to keep a strong, healthy colony. For the beekeepers with a few hives, this is an easy task – simply monitor hive activities for a few weeks (a full worker brood cycle of ~21 days) and decide if they require supplemental feeding or a newer, more active queen bee. Additionally, when it comes to storing unused frames and equipment, keeping them at temperature extremes (above 46°C or below -7°C) for at least three hours is enough to prevent eggs hatching, with the cooler option being more feasible for many beekeepers (for example, a freezer [pun intended]).
How can Beekeepers Control Wax Moths?
Female moths prefer to lay eggs in strong colonies over weaker ones (possibly due to the increased number of resource available for the larvae reviewed in Kwadha et al., 2017), yet the infestations only take hold in the weaker colonies, as there are less bees dedicated to hive defence.
As in the post on small hive beetles, this article describes the management of wax moths when keeping a strong colony is not possible. Both greater and lesser wax moths are collectively referred to as “the wax moth”, with the greater wax moth Galleria mellonella being the greater nuisance.
Steps to Prevent Wax Moths in Beehives
Wax moths cannot be “prevented” as they will always find an opportunity to enter hives. What the beekeeper can do is maintain good sanitation: seal cracks and crevices (if your bottom board looks worn, it may be time for a new one), and replace any old equipment. Old brood comb frames should be replaced (every three years is the rule of thumb), as well as any comb that starts to show sign of “galleriasis”, a condition in which newly formed adult bees are unable to leave their cells due to the silken threads produced by larvae.
In colder months or during colony downsizing, any frames/ hive products removed (wax, honey, and pollen stores) from the hive body should be stored at temperature hostile to wax moths – either at a high of 45–80 °C over 1–4 hours, or more economically, home freezers set at −7 °C to −15 °C for 2–4 hours.
These practices are easy to apply and have no negative impacts on honey bee colonies. Remember to let the frozen (or heated) frames reach room temperature before returning them the hive. However, the workload becomes tedious for beekeepers at the commercial pollination level, and are thus best suited to small-scale beekeeping operations.
Chemical Treatments for a Wax Moth Infestation
Currently, only carbon dioxide gas is recommended for use as a fumigant, being applied to stored combs under airtight conditions. This process, termed “Controlled Atmosphere Treatment” or “hypercarbia”, displaces oxygen from the air, leading to wax moth death at all life stages1. Other fumigants like sulfur, acetic acid, ethylene bromide or calcium cyanide are available, however they contaminate honey and have human health risks (reviewed in Kwadha et al., 2017).
The commonly used insecticides coumaphos and formic acid for controlling Varroa and honey bee mites are also effective in managing a wax moth infestation, however wax moth treatments would be of a lesser concern when using these chemicals.
Use of Wax Moth Traps
Commercial products are available, as well as homemade soda bottle traps. The basis of these traps, like those used to control small hive beetles, is to lure the adult moths into the container to drown. They are placed on trees or towering structures that serve as moth mating areas near the bee colonies. A clear soda bottle isn’t necessary, and any plastic jar can be used. For an example adapted from this video:
- Drill a round hole 1-2 inches in diameter on the top part of the container (say, just below the shoulder),
- On the lid, drill two holes and add string/wire or any material that can be used to support the weight of the container (this will be used to tie the structure like a tree limb),
- Heat 1 cup water, 1 cup sugar, 1/2 cup vinegar, stirring until the sugar is dissolved,
- Let the mixture cool to room temperature and place it into the container, then add in a sliced banana peel (the banana scent along with the sugars will act as the lure).
- Hang onto a tree branch or suitable structure and watch the adult moths fall into the liquid.
- How does this work? Adult moths do not eat, so what do they find attractive about this mixture… is because the banana peels mimic insect pheromones?
Biological Treatments for Wax Moth Infestations
Emerging therapies for wax moth control use targeted approaches that (largely) spare honey bees and their wax comb. Research is underway into these therapies, and many are complex, or restricted for use, except for B. thuringiensis, as you’ll read below. Sorry, backyard beekeepers.
Bacterial Treatments on Stored Comb
Ranking amongst one of the more promising organic pesticides in agriculture is Bacillus thuringiensis. B. thuringiensis has been effective against wax moth larvae; the aizawai subspecies was re-approved for use by the U.S. Environmental Protection Agency to control wax moths in 2020. The Bt bacteria produce a crystallized protein that is toxic to wax moth larvae and harmless to honey bees. The product is sprayed onto frames prior to winter storage, and any larvae that feeds on the wax comb will ingest the bacteria, leading to the production of these crystallized proteins and eventual larval death by abdominal rupture.
Parasites of Wax Moth Larvae
The parasitoid wasp Bracon hebetor (subspecies Say.) is classified in the same Order as honey bees (Hymenopetra). B. hebetor infects several species in the Lepidopetran Order, which wax moths belong to. Tests done by Adly & Marzouk (2019) showed the female wasp actively infecting wax moth larvae, stinging and injecting them with paralytic venom before laying eggs on their immobile hosts. These eggs hatch and the B. hebetor larvae feed on the wax moth’s larvae, thus completing the lifecycle. Their results showed significant decreases in wax moth larvae under laboratory, field and stored comb conditions, making it an effective large-scale biological control of wax moths.
Another parasitoid wasp species is Trichogramma evanescens (subspecies Westwood), which is already used throughout the world for controlling various moth and butterfly pests. T. evanescens targets the wax moth eggs, generally preferring younger eggs as hosts (Haque et al., 2021) (the young eggs are though to have more nutrients within the shell that yet to be consumed by the embryo). The wasp larvae hatch prior to that of the wax moth, whereby they proceed to consume the contents of the host egg, killing the developing larvae. Once the wasp larvae complete their development, they emerge as adult wasps, ready to seek out new wax moth eggs.
Release of Sterilized Adult Wax Moths
A common theme in pest control is releasing sterilised male adult wax moths. This has been used for various flies, weevils and moths, and the interested reader is directed to the Wikipedia article for further reading. While harder to conduct for the backyard beekeeper, these are potential options for a regional-level approach. Indeed, one proposed technique is to release an insecticide to reduce wax moth population, followed by the release of sterile males (Jafari et al., 2010).
Fire Ants???
While not exactly a sustainable method (they are quite aggressive…), the red important fire ants (Solenopsis invicta) in the Southern US feed on insects including wax moth larvae. This method has been particularly successful with stored comb in fire ant-dense areas- beekeepers are able to place unused combs outside in full sunlight and ventilation without fear of infestation as the ants crawl through the combs in search of larvae to consume. They’ll eat all the larvae, and they’ll also eat all the honey (but won’t mess with the wooden frame or wax!). If your wax moth infestation is that severe, delegating the cleanup process to the ants is better than doing it yourself!
Again, not recommended for your average (or even above-average) beekeeper.
Cleaning Up a Hive Infested with Wax Moths
So, your colony has been overrun or abandoned, and the moths have had their pick at this open buffet. What now? The easy and expensive answer is to discard the hive box(es); they’re ruined. A more rationale answer is:
Freeze infested frames as outlined above to kill the larvae. Once killed, remove the now-webby frames and using a hive tool, scrape off the foreign material into the garbage.
Heavily damaged frames should be discarded.
If there are a large number of larvae present, take the entire hive and place it in the chicken coop (or fire ant nest!), they’ll love the extra protein, then freeze the frames and repeat the process above.
Clean the hive box by scraping the interior with steel wool, or consider lightly scorching it with a propane torch to eliminate any lingering eggs.
Causes of Wax Moths in a Beehive
Wax moths are opportunistic pests, and in beehives they see their opportunity to reproduce and pass on their genes. When the moth eggs are laid in large quantities and large numbers of wax moth larvae is apparent, it indicates a larger, underlying issue with the bee colony, as it lacks the bee population and vigor to fend off wax moths.
Origins of Wax Moths?
The origins of wax moths are not explicitly documented, and it can be fair to assume that they co-evolved alongside bees. Indeed, this assumption can be drawn for almost any biological relationship: if two species display high dependence on one another for survival, then it can be considered a case of co-evolution. (Actionable examples of this heuristic include planting native flowers to help native bees, or consider housing honey bees in trees as this is their natural beehive).
Back to the point: Since the primary habitat and food sources of wax moth larvae are within the hive and beeswax comb, this suggests that moths have adapted into the niche of exploiting honey bee colonies. According to the 2020 review article by Wojda and colleagues, the first case of wax moth infestation was documented in the Asian honey bee, Apis cerana and had since spread globally as a result of human activities.
Lifecycle of the Wax Moth
Female moths enter the hive at night when bees are already inactive, as they would otherwise be attacked by the aggressive worker bees during daytime. Where colonies are active and healthy, the adult wax moths lay eggs as far away from the light as possible- in the spaces between combs, hive walls or the outside surfaces of bee frames. In weak or abandoned hives, the eggs are laid anywhere (shown above), with the wooden parts being used for cocoon construction. The average female moth lays around 60 eggs per day (reviewed in Kwadha et al., 2017).
Eggs hatch after 3-5 days, and this is dependent of factors like temperature and humidity2, with the average optimal wax moth larval development temperature being 29–33°C.
As larva dig into the wood to spin their pupal cocoon, they excavate boat-shaped depressions, which can weaken the entire structure of the affected part. The cocoon attaches to the depression over the course of two days, depending on the hive conditions. The cocoon acts as a shell, protecting the wax moth larva and later pupa against worker bees and other parasites (eg: a hornet inside the hive). Internally, the cocoon maintains a stable environment for pupal development; the outer layer hardens and the interior remains soft.
Depending on the temperature and humidity, the pupal stage in G. mellonella lasts from eight days (at 28°C, 65% relative humidity) to 50 around days (from 2.5°C to 24°C, 44% to 100% relative humidity). The process of eclosion, whereby the the pupa hatches and becomes an adult wax moth, occurs at night. Both males and females reach sexual maturity within a few days of emerging, and begin to mate. Males live longer (21–30 days) than females (8–15 days). Both adult moths are incapable of consuming food as their mouth parts are unformed, a common characteristic of adult Lepidopeteran species (Krenn, 2010). Mating is nocturnal and takes place near the beehive (e.g. in a tree [hence the success of the bottle traps]), and once the female is mated, she enters the beehives to begin the cycle anew.
What do Wax Moth Larvae Eat?
All the wax. Well, wax cappings, pollen and honey. They have specialized enzymes in their digestive system, like esterases and lipases (Rivera-Vega et al., 2017). Pollen provides the wax moth larvae with the protein required for larval development (to beat a dead horse, get rid of old comb!), and larvae also consume the discarded bee pupal skins as well as honey (if present).
As mentioned above, wax moth larvae will not eat honey bee larvae unless they’re starved, and in such extreme circumstances they will also cannablize their own (Nielsen & Brister, 1979). As the larvae feed, they create silken tunnels throughout the comb, which leads to that webbed, damaged appearance in infested hives.
Comparing the Greater Wax Moth & the Lesser Wax Moth
From a beekeeping perspective, the actionable items apply to both. The table below summarizes their biological aspects:
| Characteristic | Greater Wax Moth | Lesser Wax Moth |
| Size | Wingspan between 40-50 mm. | Smaller, with a wingspan 13-19 mm. |
| Adult Appearance | Dark and mottled appearance with a slightly golden sheen. | a pale, uniform grey or silver-grey colour. |
| Larvae Appearance | white with a brown head and can grow up to 28 mm in length. | also white, growing up to 19 mm. |
| Pest Activity | larvae can burrow deep into the comb, damaging both brood and stored honey. | Less destructive – larvae tend to feed on the surface of combs, especially older, dark comb (more bee skins) or pollen-storing comb. |
| Lifecycle | After mating, females lay their eggs in cracks or crevices in the beehive. The larvae go through several instar (moulting) stages, followed by pupation and emergence as adults. The entire lifecycle can take as little as 6 weeks in warm conditions, varying greatly with temperature and other factors. | |
| Preferred Environment | Found in a variety of environments but is more prevalent in areas with warm and humid conditions. | Prefer warm conditions and older comb, so more likely in long used/stored equipment. |
| Control | Regular hive inspections, maintaining strong colonies, freezing/discarding infested equipment, and proper storage methods. | |
| Egg-laying Pattern | Lays eggs in large batches, sometimes more than 100 at once. | Also in batches, but in fewer numbers. |
Bonus: Beyond Pestilence: The Greater Wax Moth as a Model Organism
Non-technical readers are welcome to skip this section
Despite being deemed a pest, G. mellonella is useful in scientific research as a model organism in studies related to infection, innate immunity, and toxicity. The greater wax moth’s innate immune system, while simple, shares similarities to that of vertebrates, and has been used to study pathogenicity (reviewed in Wodja, 2017), host-pathogen interactions (Mak et al., 2010 & Zdybicka-Barabas et al., 2015), and in vivo human pathogen testing (eg: Streptococcus A infections [Loh et al., 2013]).
The immune system of the greater wax moth has been used a source of novel antimicrobial peptides, with isolates of cecropin A (a common antimicrobial peptide in insects) being able to eradicate pathogenic E. coli-formed biofilms (Kalsy et al., 2020).
The same lipolytic enzymes for digesting beeswax can be used for breaking down plastic, and this has been demonstrated by Bombelli et al., (2017), who used G. mellonella larvae to digest polyethylene (this polymer shares a similar lipid profile to wax comb- fatty acids, esters and other carbon compounds). Further research by Ren & colleagues (2019) showed that this polymer-breakdown is mediated by the gut bacteria Enterobacter sp. and the decomposition is far faster than that of the genetically modified E. coli.
Pestilent for the hive, profitable for the human!
Discarding Old Brood Comb and Freezing Unused Frames
By now dear reader, you should know that discarding old brood comb and storing unused honey frames in the freezer is the gold standard to prevent wax moth infestation. Old, unattended comb is a fertile field for the moth’s larval stage, and they will capitalize on it. For simplicity, discard comb over three years of age (don’t be cheap – three years is good value for the few dollar it costs to make frames).
Unused frames, whether from downsizing or winter storage, should be frozen for a few days to kill wax moth eggs and either kept in the freezer or wrapped in insect-proof material and stored until needed. Last season, your humble author skipped the freezing stage and stored combs outright… he got lucky with no infestation. Next time, he may not be so fortunate.
If you’re chemically treating hives for Varroa, then wax moth (or small hive beetle) larvae are not an issue; those chemicals do a good job of controlling them. Keep healthy colonies, inspect often, and regularly replace comb in your beautiful brood box.
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Footnotes
- Death is a result of oxygen deprivation. Physiologically, carbon dioxide triggers an increase in the rate of breathing. More breathing equals more water lost through respiration, and so technically, the insect’s death is a result of desiccation. ↩︎
- Another reason to discard old comb: wax moth larvae growth was found to be faster on old combs, which contained more bee residues (e.g. skin shed from moulting) and pollen, but much slower on on new or white honeycombs. These residues in old comb contained more nutrients, particularly essential amino acids for silk protein synthesis, which resulted in the rapid growth of the larvae (Mohamed et al. 2014) ↩︎