The greater wax moth, Galleria mellonella, poses a threat to stored beekeeping equipment and weak honeybee colonies. This pest is an opportunist that targets unprotected beeswax comb, especially drawn comb that once held brood or pollen. Damage occurs during the larval stage, which tunnels through the wax, consuming the comb, pollen, and shed larval skins. The larvae leave behind silken webbing and dark, granular fecal matter called frass, which can quickly ruin entire boxes of valuable comb. If an infestation is left untreated in a warm environment, the equipment can be rendered useless in weeks, requiring immediate action to salvage it.
Immediate Eradication Using Temperature Extremes
The most direct and residue-free method for killing all stages of the wax moth life cycle involves manipulating temperature. Freezing is highly effective because it kills the egg, larval, and pupal stages simultaneously. To ensure a complete kill, comb should be exposed to -7°C (19.4°F) for at least 4.5 hours, or -15°C (5°F) for a minimum of two hours.
These duration requirements ensure the internal temperature of the comb is reached, meaning a large, densely packed stack of frames may require significantly longer to cool. Once treated, frames must be allowed to thaw completely before being placed back on a hive or stored. Condensation forms during thawing, so frames should be stored in a dry, well-ventilated space to prevent mold growth before reuse.
Heating offers an alternative method for immediate eradication, though it requires precise control to avoid damaging the wax structure. A temperature of 46°C (115°F) maintained for about 80 minutes is lethal to all wax moth life stages. Alternatively, 49°C (120°F) can kill all pests within 40 minutes.
Beekeepers must exercise caution when using heat, as the structural integrity of beeswax begins to fail near 49°C to 50°C, leading to warping or collapse. Since wax melts completely at approximately 62°C to 64°C, a carefully monitored environment is necessary to prevent permanent equipment loss. Heat treatment is often impractical for large volumes but is useful when a freezer is unavailable.
Chemical and Biological Fumigation Methods
For larger quantities of stored equipment, or when temperature control is not feasible, fumigation provides a means of control.
Para-dichlorobenzene (PDB)
One chemical option is Para-dichlorobenzene (PDB), used as a fumigant for stored equipment intended for future brood rearing. PDB is applied as crystals that sublimate into a heavy vapor, effectively killing adult moths, larvae, and pupae within the sealed stack. PDB is not consistently effective against the egg stage, so a follow-up treatment may be necessary to target newly hatched larvae.
PDB residues can be absorbed by wax and honey. Due to this contamination potential, it must never be used on comb intended for human consumption or placed on an active colony without thorough aeration. The treated equipment must be aired out in a well-ventilated area for several days before being given to bees.
Biological Control (Bacillus thuringiensis)
A biological option is a specific strain of the naturally occurring bacterium, Bacillus thuringiensis (Bt), specifically the aizawai strain. This product, often sold as Certan or B402, is sprayed onto the comb before storage. The bacterium releases a crystalline protein that is toxic when ingested by wax moth larvae.
This biological insecticide is highly selective, posing no known harm to adult bees, honey, or humans, and leaves no chemical residue. The limitation is that it is strictly a preventative measure. It must be eaten by young larvae and is not effective against adult moths or pupae.
Acetic Acid
A third option is fumigation with 80% acetic acid, primarily used to control honeybee diseases like Nosema, but which also acts as a wax moth fumigant. The acid’s heavy fumes effectively kill the egg, larval, and adult stages of the moth. It is recommended to seal stacks of comb outdoors and allow the acid fumes to permeate the equipment for about one week.
Acetic acid is highly corrosive and will damage metal components, requiring beekeepers to coat metal frame runners with petroleum jelly or use non-corrosive containers. After fumigation, the equipment must be aired for at least one week to allow the fumes to dissipate completely before being placed on a hive. The acid is less effective against the pupal stage, which is protected within its silken cocoon.
Long-Term Storage and Prevention Strategies
Once comb has been treated, proper storage is necessary to prevent reinfestation. Wax moths are naturally deterred by light and strong air movement. Equipment should be stored in a well-ventilated area that receives natural light, if possible. Stacking boxes in a cross-hatched pattern instead of flush maximizes airflow, making the environment less hospitable for the pests.
Physical barriers are highly effective at preventing adult moths from accessing the comb to lay eggs. Stacks of supers can be made moth-proof by sealing all seams and gaps between boxes with tape or by wrapping the entire stack tightly in plastic sheeting. This denies pests entry and prevents newly hatched larvae from wandering to new comb.
Storage area maintenance should include removing burr comb, wax scraps, and other hive debris, as these materials attract moths for egg-laying. Wax moths are especially drawn to dark-colored comb that has housed brood, as it contains protein-rich pollen and shed larval skins. Honeycomb that has never contained brood is significantly less susceptible to infestation.