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European Foulbrood 2: Identification and Management

Identifying and managing European Foulbrood in a Beehive

A European Foulbrood (EFB) infection may show no visible signs at times, however, sudden outbreaks often occur when the honey bee colony is under stress.

Identifying European Foulbrood (EFB)

Brood combs should be thoroughly examined for EFB at least twice a year, preferably in spring and in autumn, although EFB can occur in hives year-round.

Always remove each brood frame from the colony and inspect them individually. Clear bees from the frame and examine closely it for symptoms, paying particular attention to the colour and appearance of larvae.

Typical symptoms:

  • Uncapped cells containing sick or dead larvae will be scattered among cells with healthy brood
  • Advanced cases will have an uneven, patchy, ‘mottled’ or ‘pepperbox’ brood pattern and an ‘ammonia-like’, ‘foul’, ‘sour’ or ‘rotten oranges’ odour may be present
  • Most larvae die coiled at the base of the cell, or while turning into the longitudinal position
  • Therefore, dead EFB-infected larvae will be twisted into varied spiral shapes and can be in any position (rather than the ‘C’ shape seen in healthy larvae)
  • A small percentage of infected larvae die after capping – these caps may be dark, sunken and perforated
  • While healthy larvae have a gut line that is golden brown, yellow or orange in colour, the gut line of EFB infected larvae is chalky-white, or interspersed with yellow, white or bleached bands
  • Dead larvae will turn to yellow, then brown and become a liquefied, ‘molten’ mass
  • The trachea of the larvae may also appear a more prominent yellow colour
  • Over time the larvae remains will dry out and become dark brown, ‘rubbery’ scales that adhere loosely to the cells

Distinguishing EFB from American Foulbrood (AFB)

  • Unlike the twisted, spiralling positions of EFB-infected larvae, AFB larvae are always in the same position – stretched out on the lower cell walls, facing upwards
  • AFB infected brood will commonly have a tongue protruding to the cell roof (EFB brood rarely show tongues)
  • AFB scales are very hard to remove from the cells, while those resulting from EFB can be easily removed
  • Carry out a ropiness test at the ‘molten’ stage of infection to help differentiate between EFB and AFB

Ropiness test

Beekeepers should conduct the ropiness test to help differentiate between EFB and AFB. Carry out the test before the dead larvae dry out and reach the scale stage.

  • Identify a suitable cell with EFB symptoms
  • Push a matchstick into the cell then slowly withdraw the match
  • If the drawn out remains only form a short (usually less than 1.5cm long) thread then the disease is likely to be EFB
  • A longer ropy thread (usually around 3–5 cm) more likely means AFB
  • But, in advanced EFB infections, a secondary bacteria – Paenibacillus alvei – may infect cells and cause extra ropiness
  • This makes EFB infected brood produce a longer thread, so it can be mistaken for AFB
  • Look very closely for all symptoms of both diseases to clarify which infection is present

Additionally, in EFB cases where the secondary infection is present:

  • The larvae often lie stretched out lying on their backs on the lower walls of their cells.
  • Their colour may be reddish brown
  • Occasionally a tongue may be seen but these are not as fine a tongue as is characteristic of AFB, and rarely touch the cell roof

Even a trained eye can get the diagnosis wrong. If necessary you can get a laboratory test to confirm if the infection is European or American Foulbrood. Check your state or territory Department of Agriculture/Primary Industries website for details.

Management

European Foulbrood is a stress related disease, so stress minimisation is a key factor. Additionally, queen management and general good hive management practices by the beekeeper are all essential. Other control options suitable to some circumstances include barrier management systems and specially prescribed antibiotics.

Reducing stress

  • Common stressors for honey bee colonies include a shortage of nectar or pollen, poor weather, infestation with other pests or diseases or a failing queen.
  • Minimise movement of hives to other apiary sites, especially with a closed entrance as this particularly stresses bees
  • Avoid opening hives more than is necessary or during poor weather conditions
  • Supplement the colony’s diet with sugar syrup and fresh uncontaminated pollen when available nutrition is poor
  • Place hives in a well-ventilated, dry area where the sun is facing the entrance of the hive
  • Avoid practices that can lead to loss of heat from the hive, e.g. removing adult bees, giving extra brood to rear, or adding on supers at the wrong time
  • Reduce the volume of the brood during the winter period to preserve brood temperatures and promote a strong winter cluster

Queen management

  • Honey bee stocks can differ in susceptibility to EFB
  • This is due to differences in the hygienic ability of different honey bee strains, which is determined by the queen
  • Strong, well resourced colonies with young, prolific queens will usually eliminate the disease themselves
  • This is because shortages of cells for brood rearing promotes workers to remove sick larvae quickly
  • Colonies headed by poor or failing queens do not so readily remove diseased larvae, so the bacteria builds up in the hive
  • Always replace an infected colony’s queen bee with one supplied by a reputable breeder

Good hive management practices to reduce infection, spread and re-infection

  • If you detect EFB you should replace diseased comb with new frames, foundations and combs
  • Otherwise, as a precautionary measure, replace brood frames every 3–4 years
  • Another approach is to replace or 20–25% of old, dark comb annually
  • Reduce or prevent the exchange between colonies of hive materials (e.g. frames/comb, honey, untreated pollen) that can spread EFB
  • If you notice an EFB infection, always clean your beekeeping gear before inspecting a new hive location

Barrier management system for apiaries

  • Apiaries can put in place a barrier management system to separate hives or apiaries into different units
  • This prevents the exchange of bees, combs, honey and hive components from one unit to another
  • For commercial beekeepers, this also enhances traceability, biosecurity, quality assurance and builds on best practice principles

Antibiotics

  • Sometimes beekeepers use a specific antibiotic (Oxytetracycline) to treat European Foulbrood, but there are strict regulations to follow
  • The Australian Pesticides and Veterinary Medicines Authority register the treatment
  • Registered veterinarians prescribe it
  • The vetinarian may ask the beekeeper to supply a laboratory diagnosis of the disease, or written confirmation from an apiary inspector, first
  • However, antibiotics will only control the bacteria infecting the bees and will not treat bacteria on hive components, tools or equipment
  • Antibiotic use is also becoming less popular due to the possibility of contaminating the honey and the risk of developing resistant strains of EFB
  • The state/territory Departments of Agriculture/Primary Industries websites such as Agriculture Victoria host full details of the treatment

European Foulbrood is a reportable disease in every state and territory of Australia. If you think you have EFB contact your local state or territory Department of Agriculture/Primary Industries to make a report and get help.

Sources:

BeeAware – American Foulbrood

Rural Industries Research and Development Corporation – Australian Beekeeping Guide

European Foulbrood infected larvae can die in an position inside the cell.

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