Braula fly

Background

The Braula fly (Braula coeca) is a small species of wingless fly that lives in honey bee colonies. The Braula fly is not considered to be a serious threat to commercial beekeeping as it does not damage or parasitise any stage of the honey bee life cycle. Instead, it is considered to be a minor pest as the Braula fly larvae damage the appearance of the wax cappings on honey comb and adult Braula flies steal small amounts of food from adult honey bees.

The Braula fly is currently widespread overseas and has been reported from all continents. In Australia it is only known to occur in Tasmania. In mainland Australia, Braula fly is a reportable pest.

Life cycle

The Food and Environment Research Agency (Fera), Crown Copyright

Braula fly on the thorax of a worker honey bee. The Food and Environment Research Agency (Fera), Crown Copyright

The following is a summary of the life cycle of Braula flies:

  • Eggs are laid on various surfaces of the hive, but only eggs that are laid on capped honey will hatch.
  • Eggs hatch 2 – 7 days after they have been laid. The time required to hatch is determined by the temperature that the egg is exposed to.
  • Once the egg has hatched, the larvae tunnel under the wax cappings, leaving a narrow (approximately 1 mm wide) tunnel that is visible across the surface of the honey comb.
  • Larvae feed on honey and pollen, while tunnelling and undergo three larval stages before pupating when they are 7–11 days old.
  • Braula fly remain as pupa for 1–3 days before emerging as an adult.
  • Females mate shortly after emerging.
  • The adult then has to quickly find an adult honey bee to carry it.  Without a host to steal food from the adult Braula flies will survive for less than a day.
  • Once it has found an adult honey bee, the adult Braula fly uses specialised claws to hold onto the honey bee’s hair and rides on the bee’s thorax or abdomen. The Braula fly will move to the bee’s head to steal food while the bee is feeding itself or other bees.

Braula flies take between 10 and 21 days to develop from eggs to adults. The time required is dependent on temperature. Braula flies are able to survive in the absence of brood but require the presence of adult honey bees to survive. Adult Braula flies are thought to overwinter on adult honey bees. After conditions have become favourable again the females lay eggs and the life cycle continues.

Appearance

Lindsay Bourke

Numerous Braula flies on the thorax of a queen bee. Lindsay Bourke

The Braula fly is a small (0.9 mm wide by 1.5 mm long) wingless fly. It is red-brown coloured, covered in hairs and has six legs, which look large in relation to its body size. Braula fly lay small white eggs (0.84 mm by 0.42 mm) throughout the hive, however, only the eggs deposited on capped honey comb will hatch. Adult Braula flies can be seen on workers, drones and queens, but have a recognised preference for queen bees. In some cases queens can carry a large number of Braula fly, each of which steals a small amount of food from the queen. If enough Braula flies are present this can cause the queen to lay fewer eggs and possibly cause her supersedure.

NSW DPI

Fractured honey comb from burrowing Braula fly larvae. NSW DPI

Regular inspection of queens is a good way to detect the pest. The larvae tunnel under the cappings leaving narrow tracks about 1 mm wide, which are visible across the surface of the comb. This tunnelling gives the comb a cracked or fractured appearance, which is a key characteristic of Braula fly infestation. It is this damage that has the greatest impact on specialist comb honey producers.

Detection

Ben Oldroyd, University of Sydney

Braula flies on worker bees and numerous Braula flies on the queen bee. Ben Oldroyd, University of Sydney

Adult Braula flies are small (0.9 mm wide by 1.5 mm long), wingless, red-brown flies which can be seen riding on the thorax or abdomen of adult honey bees. Braula flies have a preference for queen bees but will also climb onto drones and worker bees. As a result of this preference, queen bees should be thoroughly and regularly checked for the presence of Braula fly.

Damage caused by the larvae is easily observed on infested honey combs. While feeding, Braula fly larvae create a narrow (approximately 1 mm wide) tunnel under the wax cappings. These tunnels are visible on the surface of the honey comb and give the comb a cracked or fractured appearance. It is this damage that affects the appearance and marketability of any comb honey produced.

For more information about detection methods click on the below links:

NSW DPI

Close up view of fractured appearance of honey comb from burrowing Braula fly larvae. NSW DPI

The Braula fly is present in Tasmania but it is a reportable pest in mainland Australia. If you notice Braula fly on your bees on mainland Australia you should report it immediately to your local department of agriculture or call the Exotic Plant Pest Hotline immediately on 1800 084 881.

Spread & distribution

The Food and Environment Research Agency (Fera), Crown Copyright

Size of Braula fly on a finger. The Food and Environment Research Agency (Fera), Crown Copyright

 

Spread

Braula fly lack wings but can be easily spread between colonies through the natural behaviour of honey bees, such as drifting, absconding or swarming, and through the movement of hives and honey bee products by beekeepers.

Human assisted dispersal

Adult Braula fly and Braula fly larvae can easily be spread through the movement of hives, as well as honey bee products, such as honey comb. This will quickly spread Braula fly amongst the apiary.

There is also a potential for queen bees and package bees to spread adult Braula fly over large distances. Buying healthy queen and package bees from reputable sources will help reduce the risk of spreading Braula fly by this pathway.

Natural dispersal

Braula flies are able to be spread through the natural behaviour of honey bees. Adult Braula flies attach themselves to adult bees, which provide a source of food and transport. Robber bees, drifting, swarming and absconding colonies can all spread Braula fly amongst an apiary, or to a new region. Once in a new colony female Braula flies lay eggs and a new infestation can occur.

The Food and Environment Research Agency (Fera), Crown Copyright

Close up of Braula fly on a honey bee. The Food and Environment Research Agency (Fera), Crown Copyright

 

Distribution

Braula fly is thought to be native to Europe. It has since spread around the world with the movement of bees and now occurs in Asia, North America, South America and Africa.

In Australia Braula flies are only found in Tasmania. Braula flies are not present on mainland Australia, and are a reportable pest in all mainland states and territories.  If you notice Braula fly on your bees on mainland Australia you should report it immediately to your local department of agriculture or call the Exotic Plant Pest Hotline immediately on 1800 084 881.

Similar pests

The Food and Environment Research Agency (Fera), Crown Copyright

Close up of Braula fly on a honey bee. The Food and Environment Research Agency (Fera), Crown Copyright

Braula fly is a small (0.9 mm wide by 1.5 mm long), wingless, red-brown fly that is carried on adult honey bees. It is a similar size and colour to the exotic Varroa mites (Varroa destructor and V. jacobsoni) and Tropilaelaps mites (Tropilaelaps clareae and T. mercedesae), and has a similar habit of attaching itself to adult honey bees. Braula fly is also similar to the endemic Pollen mite (Mellitiphis alvearius). These similarities mean that these species can be confused with each other.

The following is a description of each of the similar pests that Braula fly could be confused with.

  • Adult female Varroa mites are oval, flattened, red-brown, and 1 mm long and 1.5 mm wide.  Varroa mites, like Braula fly are carried on adult honey bees, but unlike Braula fly, the Varroa mite is capable of parasitising brood.
  • Tropilaelaps mites are active, red-brown mites which are around 1 mm long and 0.5 – 1 mm wide. Tropilaelaps mites can be seen on both adult honey bees and also parasitise brood.
  • Pollen mites (Mellitiphis alvearius) are light brown coloured and around generally smaller than Braula flies being 0.75 mm long and 0.75 mm wide. Pollen mites are not harmful to honey bees but are sometimes found in hives.
Food and Environment Research Agency (Fera), Crown Copyright

Braula fly (top), Varroa mite (right), Tropilaelaps mite (bottom) and Pollen mite (left). Food and Environment Research Agency (Fera), Crown Copyright

The presence of lines created by Braula fly larvae on the wax cappings of combs and the physical size of the adult should help to separate these species. However if you are unsure please contact your state or territory department of agriculture for further advice.

Braula fly is present in Tasmania and is a reportable pest in mainland Australia. Varroa mites and Tropilaelaps mites are reportable pests in all Australian states and territories. For more information about these pests, please see their respective pest pages.

If Braula fly is seen on mainland hives or any mites are observed on adult honey bees or in the brood, call your local department of agriculture or the Exotic Plant Pest Hotline immediately on 1800 084 881.

Management

Braula fly is present in Tasmania, but is not present anywhere else in Australia.

Generally, Braula fly is not a significant pest of honey bees. In most cases control is not required as Braula fly doesn’t have a significant impact on the colony’s health or honey yields. However, beekeepers specialising in comb honey production may need to consider control measures if Braula fly is present in high numbers during peak production periods. This is because the tunnelling of Braula fly larvae affects the appearance and marketability of honey comb.

Some simple management options exist that can control the impact of Braula fly, these include:

  • Freezing combs for at least 48 hours. This will kill all life stages of the Braula fly and is a simple method for disinfecting combs that potentially contain Braula fly larvae.
  • The normal practice of extracting honey is another effective means to control the larval stage of the Braula fly, as the larvae are removed with the caps during the extraction process. This will reduce the population of Braula fly in the hive and reduce the damage they cause for a period of time until the Braula fly population builds up again.

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:

Braula fly, Plant Health Australia

Braula fly, NSW DPI

Braula fly, University of Florida

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 Braula fly. Please be aware that some were produced overseas, and treatment recommendations or conditions experienced may differ to those in Australia.

Alcohol washing, NSW DPI and Tocal Agricultural College

Sugar shaking, NSW DPI and Tocal Agricultural College