In the rush to make increase in colonies, another result of high honey prices seems to be a rise in the incidence of American foulbrood (AFB). Complacency appears to be the culprit, as beekeepers have failed manage their colonies to control this disease.
All beekeepers in Florida are required to register with the Florida Department of Agriculture and Consumer Services. This service is the gold standard in the U.S. It provides for an annual AFB inspection. If the disease is found, the colony is required by law to be destroyed along with the bees and honey by burning, the most effective way to destroy reservoirs of infectious bacterium. The state inspection service provides a small remuneration for colonies it destroys.
Because the bacterium produces spores that can survive for many years in hostile environments, there is more danger of spreading AFB than other bee disease. This is especially true because the spores can survive in honey. Although robbing bees do spread the spores, it is probable that careless beekeepers are more responsible for outbreaks of the disease. Constant vigilance is the key, but the recent focus on making increase to take advantage of higher prices may have distracted beekeepers, allowing AFB to again become epidemic.
According to Mr. Wallingford, there is evidence that AFB, caused by the spore-forming bacterium Bacillus larvae larvae, will not develop unless more than 500,000 spores are fed to a honey bee colony. Mr. Wallingford quotes one author as saying that three possible states exist for a honey bee colony containing B. larvae spores:
“The numbers of spores brought into the colony are insufficient to infect honey bee larvae. As a result, they are not able to reproduce. The spores which are present will eventually be eliminated from the colony. These colonies are defined as not having AFB, but as being contaminated with B. larvae larvae spores.
“Adult honey bees are able to detect diseased larvae before they exhibit any visual symptoms of AFB. They may remove these larvae so that the colony will not appear to be diseased when inspected. This is the basis for selection programs that emphasize “hygienic” bees. Because larvae are being affected by the pathogen and spores are being produced, the colony is considered to have a non-clinical case of AFB. Where there are larvae or pupae in a honey bee colony exhibiting visual symptoms of the disease, the colony is defined as having a clinical case of American foulbrood.
Elimination of AFB has never been achieved on a national scale in New Zealand, according to Mr. Wallingford. It is possible, however, for the following reasons:
“New Zealand has a relatively small population of the species that is affected by the disease. There are currently just under 300,000 registered beehives in the country. There are also an unknown, but nevertheless small number of unregistered beehives, and an unknown number of feral honey bee colonies. The total number of colonies of honey bees is believed to be no greater than 400,000 in New Zealand, far fewer than other animal populations for which disease control programs were carried out.
“New Zealand is an isolated geographic area that receives no natural introductions of honey bees from outside its borders. Imports of honey bees and honey bee products into New Zealand are also restricted by agricultural quarantine measures. This makes the continual introduction of AFB into the country unlikely.
“B. larvae larvae has a low infectivity compared to many other pathogens. By destroying beehives with clinical cases of American foulbrood, carrying out proper and periodic inspections, and taking care with the transfer of beekeeping materials between hives, it is possible to reduce the concentration of spores below the level where they can become infective. As a result, the occurrence of AFB in beehives can be eliminated, even though spores of the causative organism can persist for long periods of time.
“There are a number of reported cases of New Zealand beekeepers successfully eliminating AFB from their beehives. If these beekeepers can do this, it is possible for others to do the same. A book, no sold by the Association, entitled “Elimination of American Foulbood Disease without the use of Drugs,” is contributing to this effort.
“The goal of the New Zealand program,” Mr. Wallingford concludes, “is to reduce the reported incidence of AFB annually by an average of 10 percent of the first year’s reported incidence, over the first five-year term of the strategy, and down to 0.1 percent by the end of the second term (the year 2006).”
The three keys to the success of this program are adequate inspection, proper diagnosis and the elimination of clinical cases, exactly the conditions found in Florida last year. Given the Florida experience, New Zealand’s program is theoretically possible. Maintaining the low AFB level once it has been achieved, however, will no doubt be the greater challenge.
I received some feedback on the above article above. I quoted Mr. Nick Wallingford, who said there was evidence that AFB will not develop unless more than 500,000 spores are fed to a honey bee colony. Dr. H. Shimanuki retired from the Beltsville Bee Research Laboratory states that according to Sturtevant (J. Agric. Res.:45(5), pp. 257-85), the minimum infective dose is 50,000,000 spores. There is also research in this area establishing an acceptable level of Bacillus larvae larvae spores in honey. According to Dr. Shimanuki for individual one-day-old larval feeding, the LD50 for Bacillus larvae is 35 spores.
LD50 is a statistical term; it is the level that 50 percent of tested individuals will show symptoms and die. This is not an absolute measurement because the susceptibility depends on the genetic makeup of the individual larva. Beyond this, it is difficult to infect any colony using Bacillus larvae larvae-spore contaminated honey or nectar. One reason is that neither is fed directly to susceptible-aged larvae (approximately 54 hours after egg-hatch). Larvae are only fed jelly made from worker-bee pharyngeal glands. Finally, foraging bees that have mouthparts more likely to be contaminated with the spores usually do not feed larvae.
The ability of adult bees to detect and remove larvae varies among bee stocks, according to Dr. Shimanuki. He is unable to confirm Mr. Wallingford’s source’s statement that diseased larvae are detected by workers before they show visual symptoms of the disease .
The key to American foulbrood control is inspection, Dr. Shimanuki says. It is difficult, however, to determine whether these efforts are adequate and/or cost-effective in most situations. Several levels of detection can exist, including anything from looking for spores in honey to what most inspection services do–identifying visible symptoms in the field. This also is complicated by what level of control is considered acceptable. Eradication is nearly impossible, even in a country as small as New Zealand, Dr. Shimanuki concludes. In most areas, AFB can be controlled, but beekeepers must inspect colonies more frequently, identify the disease when it is present and take corrective action immediately.