American foulbrood is a bacterial disease infecting brood of the honey bee (Apis mellifera). The disease is present in almost all countries where honey bees are found. American foulbrood was first recorded in New Zealand in 1877, 38 years after honey bees were introduced. Within 10 years, the disease had spread to all parts of New Zealand and was being blamed for a 70% reduction in the nation’s honey production.
Information on the numbers of beehives infected with the disease was not recorded during the early period of beekeeping development in New Zealand. Part of the reason was that beekeepers attempted to manage the disease, rather than destroy infected hives.
Honey bee colonies with light infections were “shook swarmed”. Bees were shaken from infected hives into hives that contained only foundation. While the method was often effective at eliminating the disease, painstaking effort was required, and some colonies still developed heavy infections and had to be destroyed.
Early attempts at managing AFB using “shook swarming” make interesting reading:
“The districts in which the Ruakura State Apiary is situated were amongst the worst in the Dominion for foulbrood. The colonies I started the State Apiary with, that were already on the farm, were affected. By constant attention and treatment we were able to keep the disease from spreading and when we left for the Christchurch Exhibition (1906) there were six out of over 70 slightly affected with foulbrood. When we returned in the following June we found the disease had spread through robbing to nearly every colony. Early in the following season we treated a number of the worst cases and replaced bad with clean combs. As this did not turn out as satisfactory as we hoped, I hoped to treat the whole of the colonies the next spring.”
In 1950, it was decided that the incidence of AFB could not be reduced further if shook swarming continued to be used. Beekeepers were therefore instructed by the Department of Agriculture to “destroy the contents of diseased hives and to sterilise thoroughly any remaining hive equipment by approved methods.”
Shook swarming is illegal in New Zealand.
Incidence of American Foulbrood Disease in New Zealand
The first reliable report on the incidence of AFB in New Zealand was in 1947,when 74% of hives were inspected by Government employees, and 1.7% were found to be infected with AFB. This was repeated in 1950 when 78% of the hives were inspected and 2.02% were found to be infected.
There were no reliable AFB disease statistics collected between 1950 and 1960. By 1961, however, the reported incidence of AFB had reduced to 0.23% of hives. The decline in disease levels during the 1950s may have been due to the move away from shook swarming (managing AFB), and the adoption of the practice of destroying diseased hives.
The percentage of beehives reported to be infected increased over the next 30 years, reaching a peak of 1.2% in 1990. During this time the New Zealand government ran and paid for the AFB disease control programme. In 1991 most of the government funding was removed and the NBA (National Beekeepers Association of NZ) instituted its own AFB control programme. The programme included the inspection of approximately 4% of the nation’s apiaries by government inspectors, voluntary inspections carried out by NBA branches (called “diseaseathons”), the counselling of beekeepers with AFB problems, a research programme elucidating the factors contributing to the spread of AFB and an extensive education programme.
During the seven years the programme was in existence, the reported incidence of the disease decreased by an average of 12% per annum, reaching a low of 0.38% in 1998, the last year of the programme. Since then, reported disease levels have fluctuated between 0.31 and 0.26%