The greater wax moth, Galleria mellonella, is a well-known species found globally, particularly where beekeeping is practiced. This insect has a long association with honeybee colonies, noted by beekeepers since ancient times.
Identification and Life Cycle
The adult greater wax moth is gray to pale brown, measuring about 15-20 mm in length with a wingspan from 30-35 mm. When at rest, its wings fold over its body in a roof-like or boat shape. Female moths have forewings with a smooth outer margin, while males exhibit a semi-lunar notch.
The life cycle of the greater wax moth progresses through four stages: egg, larva, pupa, and adult. Female moths lay their 0.45 mm long, ellipsoid eggs in clusters of 50-150 within small cracks and crevices of beehive combs or hive parts, where they are often difficult for bees to detect. Egg hatching occurs within 3-5 days at warmer temperatures of 29-35°C, extending up to 30-35 days in cooler conditions.
Upon hatching, the larvae, initially whitish with a yellowish head, begin burrowing into the wax comb. They go through seven to nine instars, growing to 20-30 mm in length and becoming grayish as they mature. The larval development period varies significantly, from 20 days in warm conditions to five months in suboptimal environments. Mature larvae spin silken cocoons, attached to hive frames or hive wood, before pupating.
Impact on Honeybee Colonies
The destructive phase of the greater wax moth is primarily the larval stage, as adult moths do not feed. These larvae consume hive components, including beeswax, pollen, stored honey, and even the cast skins of bee pupae. As they tunnel through the honeycomb, the larvae leave behind silky webbing and frass, which indicate an infestation.
These silk-lined tunnels compromise the comb’s structural integrity and can trap emerging bees, sometimes leading to starvation. Larval activity also damages cell caps, allowing honey to leak out, and can lead to “bald brood” where bees uncap cells due to larval tunneling underneath. While wax moths can be found in active hives, they pose a greater threat to weak, stressed, or diseased colonies that lack sufficient bees to defend against them. They are also a problem for stored beekeeping equipment, particularly comb not actively protected by bees.
Management and Control Strategies
Preventative measures manage greater wax moth infestations in apiaries. Maintaining strong, healthy honeybee colonies is a defense, as robust hives are better equipped to patrol and remove moth eggs and young larvae. Ensuring proper ventilation within hives and storage areas also helps deter moths, as they prefer dark, warm, and poorly ventilated environments. Beekeepers should regularly inspect hives every one to two weeks, especially during warmer months, to detect early signs of infestation.
For protecting stored beekeeping equipment, freezing frames of comb is an effective method. Freezing combs for at least 24 hours at temperatures below -6.7°C (20°F) kills all life stages of the wax moth. After freezing, combs should be stored in airtight containers to prevent re-infestation. Chemical fumigants, such as paradichlorobenzene (PDB) crystals, can also be used for stored brood comb, but strict adherence to label directions is necessary, and PDB should not be used on honey supers.
Biological control options offer another approach for managing wax moths. Certain strains of the bacterium Bacillus thuringiensis (Bt), specifically Bacillus thuringiensis subspecies aizawai, are commercially available and can be applied to combs. This bacterium is safe for bees and humans but is lethal to wax moth larvae when ingested, disrupting their digestive systems. Integrating these preventative and control strategies helps beekeepers protect their colonies and valuable equipment from wax moth damage.
Unique Biological Traits and Scientific Interest
Beyond its status as a beehive pest, the greater wax moth exhibits unique biological traits that attract scientific interest. Its extraordinary hearing ability is one such trait. Galleria mellonella can detect ultrasonic frequencies up to 300 kHz, the highest frequency sensitivity recorded in any animal. This exceptional hearing is thought to be an evolutionary adaptation, providing defense against bat predation, as bats use high-frequency echolocation calls to locate prey.
A recent discovery involves the larvae’s ability to biodegrade polyethylene plastic. Researchers observed that greater wax moth larvae can consume and break down low-density polyethylene (LDPE) films, a common type of plastic found in packaging. This degradation process results in the production of ethylene glycol, a simpler organic compound. The larvae achieve this through enzymes in their gut or saliva, which break down long-chain hydrocarbons, similar to those found in beeswax, their natural diet. This finding has opened avenues for research into bioremediation solutions for plastic pollution, though it is still in early stages and not a large-scale solution currently.