Wax moth

Background

There are two species of wax moth, the Greater wax moth (Galleria mellonella) and the Lesser wax moth (Achroia grisella). Both species eat beeswax, particularly unprocessed wax, pollen, remains of larval honey bees, honey bee cocoon silk and enclosed honey bee faeces found on walls of brood cells.

Both species are pests of active hives; however they will usually take advantage of already diseased or declining honey bee colonies and will therefore indicate to some other underlying problem(s) with the colony. Both Greater and Lesser wax moth will more commonly cause damage to unattended combs in storage, especially in areas that are dark, warm and poorly ventilated.

Life cycle

The life cycle of both species of wax moth consists of four stages: eggs, larva, pupa and the adult moths. The development of each stage of the wax moth’s life cycle depends significantly on environmental factors, particularly temperature. The optimum temperature range for rapid reproduction and development of wax moths is between 28-30oC. Light levels and ventilation also play a role.

Walter Peraza Padilla, Universidad Nacional, Costa Rica

Wax moth eggs. Walter Peraza Padilla, Universidad Nacional, Costa Rica

 

Eggs

A female wax moth starts laying eggs immediately after mating and continues for approximately 5 days. The number of eggs that are produced by the female wax moth depends on temperature, but can typically range from 300 to 600 eggs. The female lays the eggs in batches, in dark out of the way places. It takes between 3-5 days for the eggs to hatch when the temperature is between 29-35oC, and up to 35 days at 18oC.

Larvae

Susan Ellis, USDA APHIS PPQ www.Bugwood.org

Greater wax moth larva. Susan Ellis, USDA APHIS PPQ www.Bugwood.org

Once the wax moth eggs hatch the larvae immediately start burrowing through the comb of the hive and line the resulting tunnels with a silken web. The burrowing process causes damage to the cells of brood comb and honey comb. The yield and saleability of honey products can be compromised by damage to caps or the presence of the larval webbing, faeces and other debris. In brood comb, damage to cells can sometimes result in bald brood. Bald brood occurs from wax moth larvae partly removing cell caps when burrowing through the comb. Worker bees then chew the remainder of the capping and fully expose the heads of bee pupae, which can lead to deformed legs or wings in newly formed adult bees.

In warmer temperatures it can take only 20 days for the larvae to grow, but in cooler conditions it can take upwards of 5 months.  Once the larvae have grown they will find a place to pupate, which usually takes place on the wooden frames of the hive. The larvae will chew a cavity into the frame, causing permanent damage to equipment, before forming a cocoon from silk thread (2-3 days). In large numbers, the hardening of the wax moth cocoons between stored combs can cause a box of combs to become fused.

Chantal Forster

Wax moth cocoons stuck onto frames. Chantal Forster

 

Pupae/cocoon

The pupal stage involves the transformation of the juvenile larvae to the adult wax moth. The newly formed pupa inside the cocoon is initially white to yellow and transitions to be dark brown at the end of pupation. A pupa can develop and hatch within 3-8 days in warm conditions, extending to two months in cooler climates.

Adults

The life span of the adult wax moth varies depending on the sex of the moth. Females live for approximately 12 days and males can live up to 21 days. Adult wax moths do not feed for their life span. Males attract females through a combination of chemical pheromones and ultrasound signals.

Appearance

Food and Environment Research Agency, Crown Copyright

Lesser wax moth (Achroia grisella). Food and Environment Research Agency (Fera), Crown Copyright

Food and Environment Research Agency, Crown Copyright

Greater wax moth (Galleria mellonella). Food and Environment Research Agency (Fera), Crown Copyright

The adult Greater wax moth  is small and grey and about 13-19 mm long. There is some mottling on its wings, and the hind third of the wing is bronze coloured. The Lesser wax moth has similar colouration but is only 10-13 mm long. When the wings of the moth are folded over the body they appear as a ‘roof’ or ‘boat’ shape. In both species the male moths are smaller than female moths and lighter in colour. Male moths can also be distinguished by the indentation at the front of the wing, while this region is straight in females.

The eggs of the wax moth are very tiny, approximately 0.5mm in diameter, which makes them hard for beekeepers to detect. The eggs of the wax moth are pearly white to light pink at first and change to a yellowish colour during development. 

Greater and Lesser wax moth larvae can be distinguished primarily based on their size. The Greater wax moth larvae are approximately 28mm when fully grown compared to the Lesser wax moth larvae which is 13mm. The larvae of both species have a dark head with several body segments. They are initially white in colour and turn to grey as they grow.

Detection

Food and Environment Research Agency, Crown Copyright

Wax moth larvae and webbing on old combs. Food and Environment Research Agency (Fera), Crown Copyright

Food and Environment Research Agency, Crown Copyright

Wax moth silk tunnelling through brood often causes ‘bald’ brood or uncapped brood nearby as can be seen in four instances nearby. Food and Environment Research Agency (Fera), Crown Copyright

There are a number of factors which can be used by a beekeeper to detect the presence of wax moths in active hives as well as stored equipment. Wax moths will typically be located in areas of the hives where the bees cannot access, such as top bars and inner covers. Beekeepers should look for tunnels of silk throughout combs; patterns of bald brood caused by bees uncapping cells where wax moth larvae have tunnelled; and cocoons stuck to frames and parts of the hive. 

For stored equipment, look through equipment that may be kept in areas of low light, warm temperatures and poor ventilation. Beekeepers can also check for disintegrated comb and dark coloured, cylindrical faeces on bottom boards or screen trays as an indicator of the presence of wax moth larvae. When performing inspections of hives, beekeepers should be mindful of weak, stressed or queen-less colonies or unattended combs as these are more susceptible to wax moth infestation.

Spread & distribution

 

Food and Environment Research Agency, Crown Copyright

Wax moth larval tunnels through the brood often also cause damage to brood cappings. Notice the number of ‘bald’ and uncapped developing brood. The movement of hives can easily spread this pest further. Food and Environment Research Agency, Crown Copyright

 

Spread

Wax moths mainly fly at night and are able to fly between hives and cause new infestations. The pest can also be spread between apiaries by the movement of infested hives. Some research has suggested that larvae can travel more than 50 metres and therefore can move between neighbouring honey bee colonies.

Distribution

Both species of wax moth are present in all states and territories of Australia. They are a particular problem in warmer climates in the tropics and subtropics, as these areas promote wax moth activity and reproduction rates.

Similar pests

Nick Annand, NSW DPI

Close up of small hive beetle ‘sliming out’ a frame. Nick Annand, NSW DPI

Wax moth larvae are similar to Small hive beetle larvae, however there are two simple distinguishing characteristics between the two pests. Firstly, Small hive beetle larvae cause the honey to ferment and the hive to become ‘slimed out’, which does not occur when only wax moths are present. Secondly, wax moth larvae leave behind a webbing mass and tough white cocoons on the frames and hive body, which are not present when only Small hive beetle larvae are present. 

Management

The most effective method for protecting against wax moths is the honey bees themselves. It is worth noting that the wax moth can never be completely eliminated from an apiary or storage shed, so it is important that beekeepers always practice good colony management.

Food and Environment Research Agency, Crown Copyright

Honey bee attacking a Wax moth larva. Food and Environment Research Agency (Fera), Crown Copyright

 

Apiary hygiene and colony management

Beekeepers should try to keep strong colonies with high bee-to-comb ratio and a young and healthy queen bee to ensure that the bees can defend the comb against pests, including the wax moth. Beekeepers should keep their apiary clean from weak or stressed colonies, dead out colonies, or old unattended combs which provide a perfect breeding environment for wax moth. Beekeeper should also look at replacing brood combs in hives every 3-4 years.  

The removal of burr comb and propolis, as well as repairing any splits in frames will also reduce the places where wax moths can become established. Additionally, beekeepers should regularly remove the debris that accumulates on the bottom board or in the cracks and crevices of the hive, which are a good food source for wax moth larvae.

Beekeepers should also try to prevent brood production in honey supers, as the small amounts of pollen and cast honey bee larval skins are an attractive food source for wax moth larvae. Cells with a history of honey storage offer a higher level of resistance to wax moths. Old empty boxes can be cleaned with a hive tool to remove any wax moth cocoons, or a flame torch can be used (on non-plastic hive equipment) to treat areas which could harbour wax moth eggs.

Food and Environment Research Agency, Crown Copyright

Wax moth cocoons (unhatched). Food and Environment Research Agency, Crown Copyright

 

Storing combs and equipment

There are a number of non-chemical methods for maintaining empty boxes and supers of comb which can be used to ensure that they are not damaged or destroyed by wax moth larvae. Chemical treatments should be avoided due to the high risks of contaminating honey products and the honey bee colonies. Beekeepers should consider the temperature, amount of ventilation, and light levels that the combs and hive equipment are stored at in order to minimise wax moth infestation. At the right temperature the life cycle of the wax moth is very short (just over 3 weeks), so they can become a problem in stored comb very quickly. Regardless of the approach a beekeeper undertakes, stored comb and equipment should still be monitored regularly for signs of wax moth infestation to help deal with any wax moth outbreak early. 

 

 

Temperature

Comb should be stored at either very high or very low temperatures to inhibit or destroy most stages of the wax moth life cycle. Extended temperatures of greater than 46oC or below -7oC can kill all stages of the wax moth life cycle. If temperatures of 46oC cannot be accurately maintained for up to 3 hours, lower temperatures are typically recommended as higher temperatures can cause beeswax to become structurally unsound (approximately 50oC) or melt (62-64oC).

Many beekeepers have taken to storing their combs in cool rooms or freezers. Temperatures below  -7oC can kill all stages of the wax moth life cycle within 4 to 5 hours. Boxes of comb must be kept at this temperature for the required time period from the point that all the material reaches the recommended temperature. While this method is effective at killing the wax moth, the stored comb is at risk of infestation again once it is removed from cold storage. Therefore, when comb is removed from cold storage and thawing it must be inaccessible to wax moths and remain dry to prevent mould from forming. Combs that contain honey or pollen should remain in cold storage until used, unless the honey is a variety that will candy after freezing.

Light and ventilation storage

Some beekeepers have reported success at maintaining wax moth-free combs using a combination of ventilation and light measures to store their comb. This approach is simple and cost effective so long as the wax moth is not already present or established on the comb or equipment. Boxes of comb or individual frames can be stored with normal spacing in a well lit room with good ventilation. It is most effective to use an oscillating fan and constant light source to maintain the appropriate conditions.

Fact sheets

Additional fact sheets from Australia and from around the world, which provide extensive information about this pest, have been listed below. To learn more, click on the links below:

Greater and lesser wax moth, Plant Health Australia

Wax moth, NSW DPI

Wax moth, Bee Informed

Wax moth, Mid-Atlantic Apiculture Research and Extension Consortium

Wax moth IPM, Clemson Cooperative Extension

Standard methods for wax moth research, COLOSS honey bee research association

Wax moth – A pest of combs and honey bee products, Vic DEPI

Wax moth, Bee Base

Australian Beekeeping Guide (2014) Rural Industries Research and Development Corporation Publication No. 14/098 

Videos

These videos provide information about the life cycle and biology, identification and possible management options for wax moth.

Wax moth, NSW DPI

 

Wax moth control, NSW DPI