Reducing the risk of American foulbrood disease in honey bee hives
Note Number: AG1448
Published: November, 2011
American foulbrood (AFB) is an infectious, notifiable, bacterial brood disease that weakens and kills honey bee colonies. This Information Note provides information to assist beekeepers to minimise the risk of AFB occurring in hives.
AFB is a bacterial disease which is spread by microscopic spores that are too small to be seen by the naked eye. These spores remain viable for decades, perhaps up to fifty years or more.
The disease starts in a hive when honey bee larvae, less than 24 hours old, swallow AFB spores. The spores germinate in the gut of the larva to form vegetative growth that invades the haemolymph and body tissues. The infected larva dies and spores form in the decaying tissues.
As well as being present in the remains of infected larva and pupae, spores can occur in honey and pollen, and on the surfaces of combs, frames and other components of infected hives.
Reducing the risk of introducing AFB into an apiary
Buying hives that contain bees
If you are about to buy hives containing bees it is a good idea to inspect all the brood combs to make sure AFB is not present. The inspection should be done before the hives are paid for and moved to your apiary. Some beekeepers have failed to do this and have acquired and paid for diseased hives which then had to be destroyed.
The Information Note AG1426 Diagnosis of American foulbrood disease of honey bee brood provides detailed information to assist beekeepers diagnose AFB in bee hives. Confirmation of AFB can be obtained by laboratory examination of smears of infected larvae. Full details of preparing and submitting samples are found in the Information Note AG1249 Samples for Laboratory Diagnosis of Bee Diseases.
It is very important to obtain an accurate diagnosis of AFB. If you rely on a fellow beekeeper to inspect the hives for you, make sure he or she has a good understanding of AFB symptoms and knows what to look for. An inaccurate diagnosis can lead to spread of AFB throughout the apiary.
Laboratory culture tests can detect AFB spores in honey even if there are no signs of disease in the brood. If spores have been detected in honey taken from the hives to be purchased, there is a risk that AFB disease could a problem in the future.
Ask the vendor if the hives for sale have been treated with oxytetracycline hydrochloride (OTC), an approved antibiotic for control of European foulbrood. OTC does not kill AFB spores. The spores can remain dormant in the hive ready to start disease after the effect of the antibiotic has worn off.
It is always a good idea to keep hives of bees that you have purchased separate from other hives you manage. Similarly, some beekeepers who collect swarms keep them separate for several months. In both situations, inspect the brood regularly and if disease is found take steps to prevent its spread. Hive components, including combs, should not be interchanged with items from apiaries managed by other beekeepers.
Buying used bee hives (without bees) and used hive components
There is no way of knowing if AFB spores are present on or in second hand bee hive material. Similarly, the disease history of beehive components that have been in storage for many years may also never be known.
The best course of action is to have the hive material (without bees) sterilised by gamma irradiation to remove any doubt as to the disease status of the material. Gamma irradiation will make AFB spores non-viable and unable to cause disease. The sterilised components can then be safely reused.
Gamma irradiation is provided by Steritech, Dandenong, Victoria. Enquiries about this service and preparation of hive material to be irradiated should be directed to Raymond Bryden, Sales, Steritech, Victoria. Telephone: 03 8726 5514.
If it is decided not to sterilise previously used hives and components, they should be used in an apiary separate from other hives. The components should not be interchanged with those from other apiaries. The hives should be inspected frequently and if AFB is found steps should be taken to prevent its spread.
Interchange of hive comb between apiaries
AFB may be transferred from apiary to apiary when combs of honey are robbed from one apiary, extracted and then placed on hives of another apiary. Beekeepers who use a system of barrier management can avoid spreading disease. Case studies of disease barrier management systems are presented in a report entitled Honeybee Disease Barrier Management Systems. The report may be downloaded from the Rural Industries Research and Development Corporation's publications web page.
Sharing honey extracting equipment
AFB spores can be present in honey, including honey on uncapping knives and extractors used by other beekeepers. If you share extracting equipment with other beekeepers make sure it is clean before you use it. It is not necessary to sterilise the items, but all traces of honey, beeswax and propolis should be removed and the items thoroughly rinsed with clean water before use.
Feeding bees with honey and pollen
Never feed bees with honey that has not been produced in your own disease free hives. This is because honey obtained from other beekeepers and suppliers may contain AFB spores. It is safe to feed bees sugar to keep them alive when honey stores are in short supply.
AFB spores may be present in pollen harvested from infected hives. Because of this, it is a requirement of Victoria's Livestock Disease Control Regulations 2006 that pollen introduced into Victoria for feeding to bees must be gamma irradiated before or immediately after its introduction. DEPI recommends that all pollen be sterilised by gamma irradiation before feeding it to bees.
Reducing the risk of spread within an apiary
It is important that the AFB is detected early. It takes time to inspect brood and beekeepers need to know the symptoms of the disease. Brood should be inspected in early spring, in autumn before preparation of hives for winter and during the season.
In addition to checking brood, a laboratory honey culture test conducted during the beekeeping season can detect AFB spores in extracted honey. A detection of spores may mean the one or more hives in the apiary are infected or that AFB infection could occur in a hive in the future.
Interchange of hive components between hives within an apiary should not be done unless the hives are first checked for disease. AFB is easily spread through the interchange of combs and other hive components from diseased hives to healthy hives.
Hives with weak or dead bee colonies should be examined carefully for signs of AFB. When AFB is found, it should be reported to a DEPI apiary inspector within 12 hours. Steps should be taken to prevent robbing and spread to other hives and to nearby apiaries.
Bees that bring AFB into the apiary
Bees have an average foraging range of 3-5 km and this means that they may occasionally rob honey, potentially containing AFB spores, from the following:
- Weak or dead managed and feral honey bee colonies
- Unwashed honey containers disposed in the open
- Honey extracting facilities that are not bee-proof
- Infected hive material not made bee-proof.
Beekeepers cannot prevent their bees from collecting honey from these sources. However, regular inspections of brood and annual honey culture tests are the best way of detecting AFB early and minimising losses of hives, bee colonies and honey production.
This Agnote was developed by Russell Goodman, Biosecurity Victoria, Knoxfield and reviewed by Ray Gribbin, apiary inspector, Bairnsdale, in November 2011.