Wax moths: their impact and control.
Wax moth larvae are capable of widespread destruction in honey bee colonies. They consume honey, beeswax and pollen, quickly destroying comb and damaging the brood.
There are two species of wax moths; the Lesser Wax Moth (Achroia grisella) and its close relative, the Greater Wax Moth (Galleria mellonella). The latter is thought to be native to Europe and Asia, although both are common across much of the globe, having been spread unwittingly by humans. The larvae are known as waxworms, and are commercially cultivated as food for various reptiles, fish and insects. Adult Greater Wax Moths are approximately 20mm in length and are mottled grey in colouration; Lesser Wax Moths are considerably smaller and silvery-white. The larvae of the Greater Wax Moth are creamy-coloured, changing to grey as they age, and measure up to 13mm when fully grown. Those of the Lesser Wax Moth are usually white with brown heads, and are less likely to be found together in large numbers. Greater Wax Moth larvae are also recognised as useful subjects for experimental research and will explode like popcorn when fried!
Under cover of darkness, the male moths gain access to a hive and then emit a combination of pheromones and ultrasonic signals to attract a mate. In fact, the Greater Wax Moth has possibly the most acute hearing in the animal kingdom. Females lay between 300-600 small, round eggs in darkened, inaccessible areas of the hive. The entire life cycle of the moths is driven by temperature, although they also prefer a darkened, poorly-ventilated environment. Optimum temperature appears to be between 28-32oC; eggs will hatch within 3-5 days when subjected to a temperature of 29-35oC, but require up to 35 days at 18oC.
The active larvae chew through comb, creating tunnels that are lined with tough, sticky, silky webbing. This assists them to avoid worker bees. In commercial hives, yields of honey, pollen and beeswax are reduced and may be rendered unsaleable through damage or contamination with the moths’ eggs, larvae, webbing or faeces. An entire super (or box of combs) may be ruined in little more than a week. In addition, honey bee pupae may be exposed by the waxworms’ tunnelling (‘bald brood’), leading to deformities in the adult bees, and sometimes bees may be trapped in their cells by the mass of webbing. It has been estimated that beekeepers in the US alone lose US$5 million every year as a result of wax moths. Newly-hatched larvae are also
capable of infiltrating other bee colonies, as they have been shown to traverse distances in excess of 50 metres.
Under ideal conditions, the larvae mature in as little as 20 days, however this process may take more than five months in cooler weather. Often, they will damage wooden components of the hive by boring small cavities in which to form their cocoons, which are protected by the resilient webbing. The pupal stage is again greatly influenced by temperature, and may vary from about a week up to two months. Adult moths do not eat; females live for about 12 days, whereas males have a lifespan of up to 21 days.
Wax moths are far more damaging during warmer weather, and are essentially inactive during the colder months of winter. They will commonly take advantage of the reduced defensive capability of weakened, stressed or diseased honey bee colonies, which may be quickly overcome by the infestation. In healthy hives, wax moth larvae are normally evicted by workers.
The best method of control is to maintain vigorous colonies of bees and adopt an appropriate hygiene regime and other management practices. Access to hives can be restricted by screening where necessary, and debris including scraps of unrefined beeswax should be removed from the vicinity of hives, as this can form the basis of an infestation. Any affected materials should be destroyed or treated. Freezing is widely employed to safeguard or treat apiary products and materials, however some honeys may candy if exposed to these temperatures. Heat, carbon dioxide and chemicals are also used, while moth traps may have some effect.