A Pest with a History
For thousands of years wax moths have been a pest to honey bees. Today, their impact to the commercial beekeeping industry has been estimated in the millions of dollars each year.
We can read of wax moth in works by L. L. Langstroth, Francis Huber, Dr. Jan Dzeirzon and Samuel Wagner, to name but a few. These gentlemen have even noted references to the bee moth, as they were called at the time, going all the way back to Aristotle, Virgil, and Columella. In The Hive and Honey Bee, Langstroth writes that the aforementioned ancient authors recorded the bee moth “as one of the most formidable enemies of the honeybee.”
Wax moths were the leading beekeeping pests in some regions of the US until the mid-1980s, until the fateful time when parasitic mites were spread to all regions of the country.
What exactly is a wax moth and how do we prevent destruction in our hives and stored comb?
What is the Wax Moth?
Wax moths are probably best known for their total destruction of stored beeswax comb, including that stored for human consumption, such as cut comb and that created in Ross Rounds. Considering bees have to consume 8 lbs. of honey to produce 1 lb. of wax, protection of this precious resource should be a priority for beekeepers.
Larvae hide in comb, feeding on pollen, wax, honey, and occasionally brood. They can be spotted by the silk-lined tunnels they leave in the brood frames. They will remain in the hive to attach their silk cocoons to frames and woodwork, creating large gouges in the wood.
There are actually two species of wax moth – the Greater Wax Moth (Galleria Mellonella) and the Lesser Wax Moth (Achroia Grisella). These live in most areas of the United States, with the largest populations found in warmer climates, subtropics, and tropics. The Greater Wax Moth is the greater threat to our hives.
Similar to bees, the life cycle of both species of wax moth consists of four stages: eggs, larva, pupa, and adult. The development at each stage depends on environmental factors, particularly temperature. Light levels and ventilation also play a role in the transition to each new stage. The optimum temperature range for rapid reproduction and development of wax moths is between 82° F and 86° F (28-30°C).
The adult wax moth is nocturnal, spending daylight hours hidden in bushes, trees, or other sheltered places. In the evening, adult females fly to the colonies sneaking by guard bees. This is especially easy for them in weak colonies not capable of protecting the entrance, though even strong colonies are sometimes vulnerable to the passage of wax moth adults.
If a beekeeper finds adult wax moths in the hive during inspection, the colony is generally weak and this often implies other significant problems within the hive, whether pests or disease.
Reproduction
A female wax moth can lay eggs immediately after mating. She will continue to do so for approximately 5 days, laying upwards of 600 eggs. The number of eggs produced depends on temperature, typically ranging from 300 to 600 eggs. The female lays the eggs in large clusters in protected cracks and crevices. The tiny eggs are only .019 inches (0.5mm) making them nearly impossible to detect.
The eggs are pearly white to light pink, changing to a yellowish color during development. After depositing the mass of eggs, the wax moth will exit the hive in the early morning. Eggs will hatch between 3-5 days when the temperature is 84.2 – 95° F (29-35°C), and up to 35 days at 64.4° F (18°C).
Once the eggs hatch, the larvae immediately start burrowing through the comb of the hive. Often the first sign of wax moths is the presence of larvae, damage to the comb or webbing. To the untrained eye, wax moth larvae are very similar to small hive beetles. Careful identification of larvae is necessary in order to determine the best treatment options.
Both wax moth larvae and small hive beetles have 3 pairs of thoracic legs on the anterior end of the body. Only wax moths have uniform pairs of prolegs along the rest of the body. The wax moth larval body is soft and fleshy, whereas the small hive beetle larval body is rigid and hard. There are times when both pests can be found active in the same colony.
Greater and Lesser Wax Moth larvae differ greatly in size. The Greater Wax Moth larvae is approximately 1 inch (28mm) at maturity, whereas the Lesser Wax Moth is only 1/2 inch (13mm). Both species have a dark head with a white body, turning to grey as they grow.
Damage to the Hive
Wax moth larvae will consume beeswax, particularly unprocessed wax, pollen, remains of larval honey bees, honey bee cocoon silk, and honey bee feces found on walls of brood cells. As they tunnel through the comb, they will line these tunnels with a silken web. The moths leave behind a mass of webbing that small hive beetles do not.
If severe enough, the webbing in brood frames can trap bee pupae in the cells, creating a problem called galleriasis that prevents young adult bees from emerging. The burrowing of larvae causes damage to honeycomb and brood cells. Damage to the honeycomb reduces the yield of saleable products.
When wax moth larvae remove parts of the brood capping, a condition called bald brood may result. In bald brood, worker bees will remove the remaining cap exposing the pupae. This can lead to deformed wings and legs of the newly formed adult bees.
Lifespan
During warmer times of the year, it can take only 20 days for the larvae to grow. Under cooler conditions or in cooler regions it may be 5 months before they are ready to pupate. When the larvae are ready to pupate, they will excavate a cavity in wooden frames or boxes of the hive. The gouge not only causes permanent damage to the wooden ware but leaves a hiding place for other hive pests. They will form a cocoon from silk thread in approximately 2-3 days. With sufficient numbers of cocoons in a hive, the comb can fuse together as the cocoons harden.
In the pupal stage, the larvae will transform into the adult wax moth. The pupa inside the cocoon will start out white-to-yellow in coloration. They will transition to dark brown before exiting from the cocoon. In warm conditions, this can take as little as 3-8 days. Cooler climates can slow the process, extending it up to two months.
The average lifespan of the female adult wax moth is 12 days and males may live up to 21 days. The adults do not feed for their entire lifespan, as their mouthparts are atrophied. The only objectives of the adult moth are mating and laying eggs. The male will attract a female through a combination of chemical pheromones and ultrasound signals. Once mated the cycle begins all over again.
An adult Greater Wax Moth is small, at just over 1/2″ long (13-19 mm), while Lesser Wax Moths are close to 1/2″ (10-13 mm) in length. Both species can vary in color from brown to gray to black with a mottled appearance. The underside of the wings is a light gray color.
The wings are held in a folded position over the body giving a ‘roof’ or ‘boat’ shape to the moth. In both species, the male moths are smaller than female moths and lighter in color. Male moths also have an indentation at the front of the wing, not present in the female.
Identifying Wax Moths in Your Hive
There are numerous ways a beekeeper can detect the presence of the wax moth in their hives or stored equipment. Wax moths prefer areas of the hives that bees cannot access, such as top bars and inner covers. Look for tunnels of silk throughout combs. Patterns of bald brood caused by bees uncapping cells, and cocoons stuck to frames and parts of the hive are definite indicators of wax moth.
Checking the bottom trays for dark-colored cylindrical feces is a good indicator of the presence of wax moths. When performing inspections pay particular attention to any hives that are weak, stressed, queen-less or do not have enough bees to cover the comb. These hives will have a greater chance of being infested by the wax moth.
Stored equipment that has been kept in dark, warm, and poorly ventilated areas is most susceptible to wax moth infestations. The comb will generally be covered in webbing and occasionally it will have reached a point of disintegration.
Eliminating the Wax Moth
Beekeepers have many options available to them to practice integrated management of wax moths. The following choices range from non-chemical tools to chemical control. As with many hive pests, damage can be significant if the rules of control are not followed carefully and timely. The control recommendations discussed here focus on the Greater Wax Moths as they are the greater threat to bee colonies, though these methods have also been used for the control of the Lesser Wax Moths in some areas.
A treatment threshold system has not been established for the wax moth. Therefore, it is up to the beekeeper to be proactive. There are many IPM tools at our disposal for control of this pest. Chemical control should be a last resort, as there are many safer options to choose from.
Some beekeepers have zero tolerance for the moth and the slightest damage it may incur. Be wary of this philosophy, since a little damage to stored comb or in a hive can easily be repaired by the bees. After all, they are excellent comb builders.
Major damage, on the other hand, should not be accepted. This can become very costly for the beekeeper as they have to replace equipment and the labor involved to do so can be high. The cost to our bees is significant as well. They will need to expend valuable resources producing the wax needed to build new comb. This is basically the loss of surplus honey production.
Employing good beekeeping pest management practices, it is possible to avoid damage from the wax moth. But when beekeepers become careless, this pest can become a major problem, especially in stored comb.
Defending Against the Wax Moth
Maintaining strong, healthy colonies is not only the first but the most important step in defending against the wax moth. Bees that have been bred for hygienic behavior are better housekeepers, removing the debris that creates a friendlier environment for the moth.
A high bee-to-comb ratio is recommended for effective wax moth control. Any reduction in bee population or stress on a hive will allow the wax moth to gain the foothold it needs in a hive. Events such as swarming, supersedure, robbing, small hive beetles, Varroa mites, skunk attacks or over-manipulation from the beekeeper can weaken a bee colony. Once the colony’s well-being tilts in favor of wax moths, the colony is often doomed. Attention to detail when managing a hive will go a long way toward wax moth control.
Beekeepers need to carefully monitor Varroa mite detector boards and hive bottom beetle traps because they provide excellent hiding spots for the moths.
Make it a habit to always protect hive products from pests. If wax moths or small hive beetles are a problem in your area, honey should be extracted within two days of removal from the hive. If plans change, as life will often do, and honey supers need to be held longer, the beekeeper must take appropriate action to protect the honey supers from these pests.
Preventing brood production in honey supers will help avoid the possibility of any damage. Pollen and larval skins left behind from brood are far more attractive to moths than cells that have stored just honey, as they are a favored food of the larvae.
Resist the temptation of adding more honey supers than the bees can use, especially in late summer or fall. Wet supers also pose a problem if placed on the hive when wax moths are most active. During this period, they should be placed only on strong colonies for cleanup.
Trapping the Wax Moth
Currently, there are no traps marketed in the USA for control of the wax moth. A homemade trap can easily be constructed with a few items we normally have in our own homes. The trap is perfect for use in the apiary, honey house, or comb storage area, to attract and kill wax moth adults.
Start with a 2-liter clear soda bottle with a lid secured. Cut a 1 1/4 inch (3.2 cm) diameter hole in the side of the bottle just below the shoulder of the neck. Place the following ingredients into the bottle: one cup white vinegar, one cup granulated sugar, one cup water, and one banana peel.
Set the bottle aside for a few days, allowing the contents to ferment. Once the fermentation has started, hang the bottle a few feet off the ground in any of the areas noted above. The bottle can easily be suspended using a string or wire tied around the neck opposite the opening. The adult moths are attracted to the contents of the trap. Once they enter the bottle, they are unable to escape and will die.
Storing Considerations
Freshly extracted honey supers stored in a dark, warm, or poorly ventilated area is an open invitation to wax moths. Storage in tightly sealed trash bags was believed to deter these pests from damaging the comb. Unfortunately, most beekeepers learned the hard way that wax moth eggs or larvae may already be present in the equipment, and the comb can be destroyed in a few weeks.
In order to avoid this, freeze the comb first. Then allow the comb to thaw in a wax moth-free room until dry. After it has dried it may then be stored in tightly sealed bags.
Maximum use of light and ventilation is another option to control wax moths. If you only have a few colonies you can easily use this method by storing supers of comb or the individual frames in a room with very good light and ventilation. It is advised that the supers or frames be suspended from the ceiling or rafters to maximize airflow and light. If there are already signs of the wax moths on any of the combs this option is not recommended.
Commercial and larger-scale beekeepers often have specialized storage buildings to safeguard the comb against any pests. These buildings have large open windows or no sides, allowing for unobstructed airflow. Some buildings also use air circulation units to ensure maximum airflow. Frames are stored on special frame holders or hung from the ceiling at least one inch apart. Supers of drawn comb are stacked with a minimum of the one-inch distance between each super.
Temperature is another form of physical control that allows for rapid, safe, and effective wax moth protection. This is an excellent method for storing extracted comb or hive products intended for human consumption, such as comb honey or pollen.
When a few frames of a bee colony are found to contain wax moth larvae they may be frozen to kill the larvae. This will also kill any brood present on the frame, so it is not an option for a colony with a large-scale infestation. In fact, a large-scale infestation or weak colony is a sign of a serious problem within the hive. The primary problems such as queen failure, mites, or disease must be addressed. The frames may be returned to the colony once they have thawed out.
A standard household freezer will work for the hobbyist beekeeper, as long as sufficient time is given to kill all life stages of the wax moth. In honey extracted comb, the required time and temperatures are 19.4°F (-7°C) for 4.5 hours, 10°F (-12°C) for three hours or 5°F (-15°C) for two hours. These times need to be increased for comb honey or if you are filling a freezer to capacity with comb. It is always best to err on the side of caution.
Heat can be used to kill all life stages of wax moths in comb containing little to no honey. The exposure times and temperatures for heat are as follows: 115°F (46°C) for 80 minutes or 120°F (49°C) for 40 minutes. Timing for treatment does not begin until the desired temperature is reached. DO NOT heat combs above 120°F (49°C) because they will sag above this temperature and beeswax melts at about 148°F (64°C). Frames should be heat-treated only in the upright position and should not be handled until allowed to cool (Shimanuki and Knox 1997).
Some final steps that may be taken to reduce wax moth problems include: keeping bottom boards in live colonies clean, as wax moth larvae can hide in the debris; old empty boxes should always be scraped clean with a hive tool to remove any overwintering wax moth cocoons; and finally burning damaged comb which may still harbor wax moths.
Biological Control
There are currently two well-known biological control options. B401 is a microorganism, manufactured by Vita-Europe Ltd. for control of wax moths, but it is not currently registered for use in the USA. The other option, occasionally employed by southern beekeepers, is fire ants.
B401 is a bacterium, Bacillus Thuringiensis Subspecies Aizawai, manufactured specifically for wax moth control in stored comb. It will leave no residue on the comb and is harmless to bees and humans. The product must be applied before there is an infestation as it works by killing larvae feeding on comb.
There are other strains of Bacillus Thuringiensis that are toxic to bees and humans. Beekeepers must resist the temptation of using other BT products.
Several years ago, B401 was available in the USA under the trade name Certan®. One application of the product gave wax moth protection in stored comb until the next season. B401 is currently available in Canada and some European countries. There have been discussions that this product may become available in the USA again, but currently, it is illegal to purchase or use this material in this country.
Red imported fire ants (Solenopsis Invicta), which are now found in nine southeastern states in the USA, parts of Oklahoma, and Puerto Rico, are natural predators of wax moths. They currently infest over 275 million acres, creating large networks of underground tunnels. Their tunnels radiate from the mound covering several meters of the foraging area.
Some beekeepers in the southern USA store their supers of drawn comb on wooden pallets allowing adequate light and ventilation along with fire ants to control the wax moth.
Research at Clemson University has shown that a high degree of wax moth control (practically 100%) in stored equipment can only be achieved in areas of extreme fire ant activity. However, storing extracted comb on a site or outyard, where a few fire ant mounds are present, should offer the beekeeper an acceptable level of wax moth control.
Always make sure the comb has been fully extracted and cleaned out by the bees. Otherwise, the fire ants will feed on the honey and possibly damage the comb.
Beekeepers who are allergic to fire ant venom are not advised to practice this form of wax moth biocontrol!
Chemical Control
Chemical control of wax moths in an integrated pest management program should only be used as a last resort. Only when other options have failed or are not possible should the following chemicals be used. The two chemicals available in the USA to control wax moths are paradichlorobenzene (PDB) and aluminum phosphide (Phostoxin).
PDB
PDB may only be used for protecting stored comb from wax moths. It is not registered for use in live bee colonies, nor is it approved for the protection of comb honey. PDB is a crystal that forms a vapor when temperatures rise above 70°F (21°C). As honey absorbs PCB fumes it would be unfit for human consumption.
Five supers or ten half-depth supers are stacked vertically in a beehive fashion. Any cracks or openings are securely closed off with tape to provide a good seal. As instructed on the product label, 3 oz or 4 tablespoons (85 g) are placed on a piece of paper or cardboard that has been placed on the top bars of the top super. Cover the hive with the lid again making sure any opening is securely sealed with tape. The vapors are heavier than air and will sink down through the stacked supers.
PDB will kill wax moth adults, larvae, and pupae. The vapors also repel wax moths from entering exposed equipment. However, the vapors will not kill wax moth eggs. Crystals vaporize quickly at warm temperatures and have to be replenished periodically if the equipment is stored for any length of time.
Equipment must be aired out for a day or two prior to placement on colonies because it is toxic to bees at high concentrations.
Mothballs that contain naphthalene are not registered for wax moth control and are illegal for use in protecting beekeeping equipment.
Aluminum Phosphide
Aluminum phosphide is sold under various trade names and is only available for purchase and use by licensed pesticide applicators. It is a fumigant for control of wax moths in stored drawn comb. It is flammable and can be extremely hazardous to humans.
Beekeepers should never use off-brand or unregistered chemicals for wax moth control. The risks are great when a beekeeper breaks the law (federal and state) when using a product or chemical not registered for a specific pest. Beeswax readily absorbs chemicals and may harbor toxic materials for long periods of time. Use of illegal chemicals may lead to contaminated hive products, resulting in injury to the consumer as well as the beekeeper.
The wax moth can never be completely eliminated from an apiary or storage shed, so it is important to always practice good colony management. Integrated pest management will benefit the bees and beekeepers. As discussed, we have many tools at our disposal to control the wax moth in the living beehive and stored comb.
Keeping strong and healthy colonies is always the first defense against any pest or pathogen our bees may encounter.
Author
Sources
Texas Apiary Inspection Service
Hoopingarner, Roger Ph.D. (2006). Langstroth’s Beekeeping Classic
