Diseases

Pests and diseases which must be reported


As far as we are aware, the following pests and diseases are not seen on the Island. Let’s keep it that way but be prepared to report any instances to DEFA Animal Health without delay (685844). If you are unsure you should call your local Association for a second opinion. It is always good practice when visiting other apiaries to minimise risks of spreading disease etc to sterilise your hive tool and wear new or sterilised gloves. Dirty bee suits are also a no-no.

Below is a brief description of each of the pests and diseases which must be
reported to DEFA.

  • American Foul Brood

  • European Foul Brood

  • Varroa

  • Tropilaelaps mite

  • Small Hive Beetle

Foul Brood – American and European

The term ‘foulbrood’ covers two diseases of honey bee larvae; American foulbrood (AFB) and European foulbrood (EFB). Both are present in the UK and considerable economic damage is done to the beekeeping industry every year.

European foulbrood (EFB) is caused by the bacterium, Melissococcus plutonius. The bacteria is a gut pathogen and causes the death of a proportion of the larvae infected. Bacteria enter the digestive tract through contaminated brood food. Once the larva dies, it begins to turn yellow and lose its healthy segmentation pattern, some say it ‘melts’. The larval remains will dry up leading to dark brown ‘scales’. The gut of an infected larva may be visible through its translucent body wall. It has a creamy colour caused by the mass of bacteria living within it. Infected larvae are yellow looking next to normal pearly-white larvae and will not be sitting neatly in their cells in the healthy ‘C’ state. With a heavy infection with EFB, the brood pattern will become patchy and erratic as dead brood is removed by the nurse bees.

American foulbrood (AFB) is caused by a spore-forming bacterium called Paenibacillus larvae. As with EFB, this bacteria is a gut pathogen, but unlike EFB, it is extremely virulent and will kill 100% of infected larvae. AFB can form spores, which are a dormant but very resilient and can survive extremes of temperature and humidity. This means that AFB spores can be difficult to eliminate. Young honey bee larvae become infected when they consume P. larvae spores in their food. AFB generally affects only sealed brood. When infected larvae die within the sealed cells, the appearance of the cell capping changes. Cappings become sunken and dark as the developing brood inside die. Some cappings may be moist or greasy-looking and may show signs of nibbling where the nurse bees have tried to
remove the dead larvae. As more sealed brood becomes affected, the brood pattern will become patchy or ‘pepper pot’ in appearance and there may then be an unpleasant smell associated with decomposition. If a matchstick is inserted into a suspect cell with a dark, slimy looking cell capping and slowly withdrawn, the remains can be drawn out in a brown, mucus-like thread or ‘rope’ 10 – 30mm long which is a reliable test for the presence of AFB.

With EFB, the bees can be shaken into a fresh hive. Frames that have been in contact with EFB must be destroyed as the wax may contain the bacteria. Boxes must be scorched with a blowtorch.

AFB infected colonies must be destroyed completely to prevent further spore production; this includes infected frames and wax. As AFB spores are persistent in the environment, meticulous disinfection of the apiary is needed after infection.

Swarms are potential spreaders of foul brood and in risk areas should be hived away from the apiary until you are sure the new colony is free of disease.

Other brood problems
There are several other brood diseases and disorders that, although much less serious than foulbrood, are widespread but do not need to be reported. It is essential to be able to recognise these and distinguish them from foulbrood.

Sac brood is caused by a virus but signs can be mistaken for AFB if it takes hold. The larvae are ‘gondola’ shaped as the virus prevents them from shedding their last larval cuticle (skin), causing fluid to  accumulate between the body of the larva and its unshed skin, resulting in death. The colony should be able to handle the infection
without intervention.

Chalkbrood is a caused by a fungus Ascosphaera apis. It grows best at temperatures slightly below that for optimal brood rearing. Chalkbrood is often associated with chilled brood. Chalkbrood is fatal to infected larvae and can result in a decline in bee numbers but it does not typically cause the demise of a colony. The fungi germinate in the larval gut when the colony temperature falls below 32°C for more than two hours. Drone brood often at the periphery of the brood nest and more likely to become chilled is often susceptible. Infected larvae will initially be covered by fluffy, white fungus and then dry out and shrink down to form a distinctive ‘mummified’ chalk-like appearance.  Workers will uncap and remove the majority of infected cells leading to an uneven ‘pepperpot’ appearance of the comb.

Varroa

Varroa destructor is a parasitic mite of honey bee brood and was unknown in the British Isles until 1992. It has since spread to all but the most isolated islands.

Adult female mites have flat, reddish-brown, ovalshaped bodies and measure approximately 1.6 mm by 1.1 mm and are readily visible on bees. The mature female mite enters an open brood cell, just before it is capped. As well as feeding off the growing pupae, the mite is also responsible for vectoring deformed wing virus (DWV) to further deplete the hive’s strength. The mites feed on their host through punctures made with their sharp mouthparts into the fat bodies within the abdomen of the bee.

Monitoring involves inspecting base debris, using meths to suspend it where the debris sinks and mite bodies float or else decapping drone cells with an uncapping fork and looking for mites against the white of the bee pupae. Shaking a handful of bees in alcohol to remove and assess the mite numbers seems rather drastic while rolling bees in icing sugar to remove the mites for counting just makes the bees a tad disorientated. If it gets here, Varroa treatment would in involve acaricides like oxalic acid which is not very pleasant to either bees nor humans.

Tropilaelaps mite

These mites are native to Asia and have spread from their original host, the giant honey bee to Apis mellifera. There is a serious risk of their accidental introduction into the UK. Import regulations are our best defence.

Tropilaelaps mites are damaging parasites of immature honey bees. Adult mites lay their eggs on honey bee larvae inside their brood cells. These hatch into mite larvae that feed on the haemolymph (blood) of developing bees. Tropilaelaps cannot stay alive during the winter where colonies are broodless. However, in warmer areas, where colonies have brood, even in small amounts, all year round, the mites would survive.

The mites are reddish brown, about 1mm long x 0.5mm wide with a life cycle similar to that of Varroa. Varroa mites are larger, crab-shaped and wider than they are long, The body of Tropilaelaps is elongated and it is a fast-running mite. Damage is similar too, with irregular brood patterns; stunted adults with deformed wings and  shrunken abdomens. Their reproduction rate is faster than Varroa but the adult cannot survive outside sealed brood for more than a few days, so this weakness can be exploited to control it.

Monitoring is the same as for Varroa – inspect base debris using meths to suspend it where the debris sinks and mite bodies float, decapping drone cells with an uncapping fork and looking for mites against the white of the bee pupae. If it gets here treatment would in involve acaricides as against Varroa.

The bee louse, Braula coeca, is a wingless fly that lives harmlessly on adult bees but may be confused with Varroa as they are similar in size.
It can be distinguished by its more rounded shape and by its six legs that are visible on both sides of its body.

Small Hive Beetle – Aethina tumida


The small hive beetle (there are larger species in Africa) was not identified outside Africa before 1998 when it appeared in Florida. It is  now present in Italy but so far has not been reported in the UK. African bees have natural defences built up over centuries and can cope with an infestation but here the beetle would multiply to huge numbers within infested colonies, where it eats brood, honey and pollen, destroys combs and causes fermentation and spoiling of honey. If beetle infestations are uncontrolled they ultimately destroy the colony.

Larva with three distinct pairs of legs towards the head and spine on their backs are 10-11mm long. Adults are black, 5-7mm long and will scuttle away from the light.

Asian Hornet

The Asian hornet, Vespa velutina, is now increasing called the yellow  legged hornet after one of its distinguishing features. It arrived in
Europe in 2004 and has since spread as far as the Channel Islands and it is thought that an early example found in Kent in 2024 may have overwintered there. Nests have been reported as far north as Hull so the threat is getting closer.

It is slightly smaller than the European hornet but that is not present on the Island so the best comparison is a huge, noisy wasp. The queen is some 30mm long. The hornet has an orange face and the abdomen is mostly black except for the fourth abdominal segment which has a yellow band. It can be mistaken for the harmless wood wasp but the latter has a distinguishing long ovipositor at the end of its abdomen.

The hornet prowls close to the entrance of bee hives and predates on a flying bee. It takes the muscly thorax back to its nest to feed protein to its young. The only effective control is to destroy its nest which are often high up in trees. Bait stations are set, flight directions are noted and timings to return taken. The bait station is moved to get closer to the nest in a time-consuming tracking exercise. Continental bee hives can be protected to some extent by elaborate barriers.

Sightings must be reported to DEFA without delay.

Wax Moth

Not notifiable but a nuisance nonetheless.

Wax moth infestations are caused by unhygienic management practices; leaving scraps of burr comb lying around the apiary and  empty and exposed supers or brood boxes with drawn comb in will attract moths. When the equipment is left over a long period of time, this gives ample opportunity for infestations of wax moth to get out of control. Drawn comb is damaged and eaten away, making in  unworkable by the bees.

Certan (B402) larvicide is no longer sold as a preventative treatment for stored comb so the best method of control is to place drawn frames in the freezer for 24 hours and seal effectively for storage. Outside storage of frames during the winter is effective particularly if there is an early frost.

We only see lesser wax moth on the Island and they do not spin a web but rather tunnel through the comb leaving their excrement.

The notes above were largely distilled from the National Bee Unit website from where you can download more exhaustive advisory leaflets. (www.nationalbeeunit.com/diseases-and-pests)