American Foulbrood

by Ray Lackey American Foulbrood (AFB) is probably the most feared of honeybee diseases. It is caused by a spore-forming bacterium, Paenibacillus larvae (P. larvae) that infests the brood and kills it in the pupa ...

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by Ray Lackey

American Foulbrood (AFB) is probably the most feared of honeybee diseases. It is caused by a spore-forming bacterium, Paenibacillus larvae (P. larvae) that infests the brood and kills it in the pupa stage. The hive is very dependant upon the continual replacement of aging and dying bees, since their normal lifetime is only six weeks, so this disease quickly leads to colony collapse. Often the equipment is just stored away and used again later to repeat the cycle. Each time the disease goes unidentified, local bees are able to rob the colony of its remaining food reserves, thus carrying the spores home to infect their own colony, and to further the spread of the disease.

There is no cure for the disease, although treatment with Terramycin can mask it. The spores can remain viable for over seventy years. We only know that they can remain viable for over seventy years because that is the oldest documented sample we have and it is still going strong. Diagnosis by the hobbyist is difficult and it is often confused with European Foulbrood and chilled brood. Meanwhile, one larva succumbing to AFB infection produces 2.5 billion spores.

We have had pockets of recurring infestations of AFB for many years on Long Island. It has often been assumed that there was a beekeeper, not recognizing the disease or masking it with Terramycin, or an infested bee tree, hosting the reservoir of spores for reinfestation. With the appearance of mites on Long Island, most of the wild bees and the bees of several beekeepers were wiped out. Wax moths quickly destroyed their remaining comb and possibly helped reduce the spore-reservoir attractiveness. In any case, we have had several years with little occurrence of AFB.

The last few years has allowed some resurgence of the wild honeybee population because of increased resistance to the mites within the current domestic hives and their cast swarms. These swarms are possibly reoccupying the old nest sites hosting the AFB spores and building new comb. Unfortunately, the nest walls and the debris at the bottom of the nest cavities can still contain billions of spores that can be picked up by the bees during cleanup and cause a reinfestation. The unprotected food reserves that remain as the colony collapses become an attraction to the local bees, thus starting the cycle over. Although this is only a theory put forth to researchers and other beekeepers, no one has found a flaw to its potential, and we are seeing resurgence in AFB to alarming levels.

New York State requires that colonies identified as infected by AFB be killed and the equipment be burned. It can thus be a significant loss to the beekeeper. Some states allow treatment with Terramycin to suppress the disease but the hive cannot be used for production of honey when being medicated. Such equipment is also banned from interstate transport. The spores can be killed by high heat, ethyl-oxide combined with heat, and gamma radiation. Some states and other countries accept one or more of these as method of eradicating or as a prophylactic treatment for the disease.

The big difficulty for the hobbyist is knowing when he has a problem. The USDA considers this disease of significant danger to the country's agriculture industry and performs diagnoses on supplied samples of comb at no cost. Unfortunately it can be a couple weeks between the submission of the sample and the response, and no one wants to wrongly burn his own or someone else's equipment, thus allowing the disease to spread. What is needed is a rapid confirmation of the diagnoses.

I recently attended a short course on Integrated Pest Management (IPM) for Honeybee Pests offered by Cornell University. One of the most important things I learned from that course was how to conduct the Holst Milk Test for AFB. This is a quick test yielding results within half an hour that can be run with ingredients found in your kitchen or at the corner deli. I was nothing short of amazing.

I don't understand all of the chemistry of it so let me quote from the USDA handbook "Diagnosis of Honey Bee Diseases", Agriculture Handbook Number 690. "The Holst milk test (Holst 1946) is a simple test based on the high level of proteolytic enzymes produced by sporulating P.Larvae. The test is conducted by suspending a suspect scale or a smear of a diseased larva in a tube containing 3-4 ml of 1-percent powdered skim milk in water. The tube is then incubated at 37 C. If AFB is present, the suspension should clear in 10 to 20 minutes. It should be noted that this test is not always reliable."

Lets handle the disclaimer first. It is generally considered reliable to confirm the disease. If a negative test results, a lab test may still be justified. The test should be run with some duplication and controls to allow for the errors of home testing. It will work on a freshly killed larva or a scale several years old. The spore forming bacteria P. larvae produces proteolytic acid, which reacts with the skim milk. Set up multiple test tubes with one Tablespoon of skim milk and inoculate some while keeping one for control. Incubate in hot water for twenty minutes and check periodically. If the culture clears while the control stays cloudy, you should notify the local fire department that you are having an outside bonfire that evening, they are welcome but please bring your own hot dogs and sticks!

Actually, due to the burning laws on Long Island, we approached the state several years ago and asked for a reprieve on the rule that said that the hive had to be killed and burned on site. We have been allowed to double bag the equipment in plastic garbage bags and transport to a local incinerator where we should witness the burning. I wish you healthy bees but if in doubt about what is killing your bees, consider the Holst Milk Test!

I will plan on demonstrating this test at the next meeting of the Long Island Beekeepers Club to be held in February 2001.