The greater wax moth, Galleria mellonella, is a common insect that poses a significant threat to beekeeping. Understanding its life cycle is crucial for effective management and prevention of infestations. This article delves into the biology, behavior, and control methods associated with G. mellonella, providing insights for beekeepers and researchers alike.
Galleria mellonella, also known as the greater wax moth or honeycomb moth, belongs to the family Pyralidae. Its global distribution makes it a ubiquitous pest for beekeepers worldwide. The larvae of this moth can cause extensive damage to honeybee colonies, costing the beekeeping industry millions of dollars annually.
Originally reported as a pest in Asia, G. mellonella has spread to various regions, including northern Africa, Great Britain, parts of Europe, northern America, and New Zealand. It has been documented in numerous countries across Africa, Asia, North America, Latin America, Australia, Europe, and several island nations. This widespread distribution highlights the moth's adaptability and its significant impact on global beekeeping practices.
G. mellonella undergoes a complete metamorphosis with four distinct life stages: egg, larva, pupa, and adult.
Females lay their eggs shortly after emergence in the small cracks and crevices inside a beehive. They prefer to lay their eggs in strong, healthy bee colonies over weaker colonies, The smooth, spherical eggs are small, ranging from 0.4 to 0.5 mm in size, and are laid in clusters. The incubation period varies depending on environmental conditions, typically ranging from 4 to 10 days.
Once the eggs hatch, the larvae immediately start burrowing through the comb of the hive. The larvae, also known as waxworms, range in size from 3 to 30 mm long and are white or dirty gray in color. They feed on the midrib of the wax comb, cast skins of bee larvae, pollen, and small quantities of propolis and honey. The tunnels they create are lined with silk, which entangles and starves emerging bees, a phenomenon known as galleriasis. Feeding is more intense during earlier instars compared to later instars. They can remain in the larval stage anywhere between 28 days to 6 months, during which they undergo eight to ten molting stages. Cannibalism has also been observed in food shortages.
When the larva is ready for pupation it moves either to the wood of the frame or the box itself and chews a cavity in which it begins spinning the cocoon. The pupa inside the cocoon will start out white-to-yellow in coloration and 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.
Adult moths are brown gray and range from 10 to 18 mm in length. The adults' wingspan is 30 to 41 mm. Adult moths do not feed at all and their only goal before death is to mate. Female wax moths live for 12 days while the males live longer, up to 21 days. Males call for females with ultrasonic sound pulses that attract virgin females and initiate courtship. After the initial greeting the male emits a pheromone that starts the mating process. This moth flies from May to October in the temperate parts of its range, such as Belgium and the Netherlands.
Males call for females with ultrasonic sound pulses that attract virgin females and initiate courtship. Once females get closer, males produce a sex pheromone to initiate mating. There are many known kinds of sex pheromone including nonanal, decanal, hexanal, heptanal, undecanal, 6,10,14 trimethylpentacanol-2 and 5,11-dimethylpentacosane. It is also known that these pheromones are often used to create traps to attract females. Males generate ultrasonic sound pulses at 75 kHz, 200μs per pulse that are used to attract females for mating. This is generated by twisting an end of the tymbal, the membrane that produces sound in insects, with the wings.
Both sexes are equipped with a sensitive tympanic hearing organ that allows the great wax worm to perceive high frequency sound. This likely resulted from selective pressure from insectivorous bats; being able to detect their echolocation would enable G. mellonella to avoid being eaten. Female tympanic membranes are 0.65 mm across; males’ are 0.55 mm across. Emitters that produced ultrasonic sounds at similar frequencies as echolocation prompted G. mellonella to tilt their head and then exhibit dropping, looping, and freezing behaviors, all of which are meant to evade predators. The head tilt was a direct response to sound reception; once tympanic hearing organs were destroyed, this response was lost. Notably, predator evading behaviors were not exhibited when G. G. mellonella seems to be able to differentiate between different frequencies and pulsing patterns. It has been hypothesized that G. mellonella use the 30-100 Hz range for communication with other members of its species.
This species of moth is a major parasite of the wild and cultivated honey bee, costing millions of dollars of damage each year. It is said to be present in any area where beekeeping is practiced. The tunnels they create are lined with silk, which entangles and starves emerging bees, a phenomenon known as galleriasis. Tunnels also result in massive destruction of the combs. As a result, honey is wasted as it leaks out when cell caps are eaten. Finally, both G. mellonella larvae parasitize wild honeybees.
In order to prevent or manage infestations, cultivators are encouraged to maintain sanitary conditions for their bees, as it will keep the colony strong so they can keep G. mellonella out. Cracks and crevices should also be sealed so that adult G. mellonella cannot lay their eggs there.
Temperature treatments also destroy G. mellonella at all stages of its life cycle. Heat treatment keeps the combs and beekeeping equipment at 45-80 °C for 1-4 hours, or in hot water for 3-5 hours. However, heating at this temperature can cause sagging and distortion of the wax. A standard household freezer will work for the hobbyist beekeeper, as long as sufficient time is allowed for the items to completely freeze. Sealing the clean, dry comb in airtight bags or containers after freezing can prevent re-infestation.
Chemical fumigants also destroy all stages of G. mellonella and are economically convenient. Avoid chemical deterrents like mothballs and para-mothballs as the chemicals responsible for the deterring effect have been labeled as cancer causing by the State of California and direct access to the combs can contaminate the honey product.
Usage of gamma radiation to sterilize male pupae, or the male sterilization technique (MST), has also been used to control Galleria mellonella populations.
Apanteles galleriae parasitizes G. mellonella larva inside the beehive. 1-2 eggs, laid by the adult Apanteles galleriae, were found on each larva, with only one successfully parasitizing the host and surviving throughout its life cycle. The parasite emerges and ruptures the host body, and pupates into a small cocoon. Parasitism increases gradually, starting in February, reaching its peak in May, then declining until July. However, it is unlikely that this parasite will take root in a strong, healthy colony as they will be kept out of the hive by bees. Habrobracon hebetor also parasitizes G. mellonella adults, along with other members of the family Pyralidae.
The best deterrent to wax moths is an active, healthy and vigorous colony. The bees should only have as much space as they can effectively defend and that means removing extra or unnecessary boxes and dead outs from your apiary as soon as possible. Store your comb in areas that get light and have ample ventilation at least until winter (if it freezes regularly in your area) when you can move your boxes to a shed or barn until spring. If that is a problem for you, I have had success moving boxes into airtight lawn debris bags and sealing them with duct tape.
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.
The waxworms of the greater wax moth have been shown to be an excellent model organism for in vivo toxicology and pathogenicity testing, replacing the use of small mammals in such experiments. The larvae are also well-suited models for studying the innate immune system. In genetics, they can be used to study inherited sterility (cellular and humoral immunity are part of acquired immunity, which is only in vertebrates.
In 2017 it was shown that the larvae could degrade polyethylene. Recent research by Dr. Polyethylene is one of the most difficult plastics to break down.
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