Geoff Heathcote-Marks, Dominique Marchand and Geoff Tribe
American Foulbrood (Paenibacillus larvae) is an exotic bacterial disease which appeared in South Africa some 20 years ago and to which our indigenous honeybees had not before been exposed. After its initial discovery in the Cape Peninsula where it wreaked havoc amongst several commercial beekeepers, the disease spread throughout the Western Cape where sporadic outbreaks were reported over the intermediate years. Then in 2015 there was again an upsurge in the disease in which major losses were inflicted on mainly commercial beekeepers which raised major concerns.
The economy of the Western Cape is underpinned by the export fruit industry which in turn is reliant on pollination by honeybees. With the expansion of the industry in recent years, there is already a shortage of pollination units. This is now exacerbated by the presence of American Foulbrood (AFB) which is only contained either by incinerating infected hives or by radiation treatment which adds to the cost. Why commercial beekeepers are more adversely affected by American Foulbrood as compared with that of hobbyist beekeepers appears to be the greater mobility of hives of the former and the higher infection rate experienced at the depot where honey is extracted due to intermingling of hive parts and the drifting of bees.
Hobbyist beekeepers in Pinelands
The recent discovery of American Foulbrood in the Cape Town suburb of Pinelands has raised some interesting questions. Several hobbyists keep hives within the suburb and there are many wild swarms to be found both within trees and in air vents etc. in houses. Swarms are trapped or removed within and in the surroundings of the suburb but there is no commercial activity where hives are taken to orchards for pollination purposes. The suburb provides many flowering plants for the bees to utilize including ornamental eucalypt species such as the red flowering gum, Corymbia ficifolia (Fig.1), the sugar gum Eucalyptus cladocalyx and many other tree species such as the Brazilian pepper tree. Garden flowers and indigenous plants in many open spaces provide both nectar and pollen especially in spring, but there is always something flowering throughout the year.
Several incidences of AFB infected hives have been recorded in Pinelands both in hives and in wild swarms. The current case has been well documented. The bees took up residence in an owl-box at a height of 6 metres from the ground in late November 2014. Here they flourished for about a year. However, they were observed to abscond on 30 December 2015, settling in a tree for a brief time before disappearing in a swirl of bees. They left behind about 8 sturdy combs about 22 cm deep and wide, of which 4-5 had been brood combs. All the honey had been consumed by the departing bees. Some diseased brood which had the typical sunken appearance and perforations in the cappings together with the characteristic scattered brood pattern (Fig.2) remained to show the extent of the disease. The ‘matchstick’ test confirmed the presence of AFB (Fig. 3).
What raised many questions were the following observations. Although there were two hives on the property, no robbing of the vacated owl box was observed – which raises the question whether the smell or sliminess (Fig. 4) of the infected combs act as a deterrent to potential robbers? If this were so, it would serve to help contain the spread of the disease to a great extent. This foul odour which is symptomatic of the disease is foreign to African bees, and if it acts as a deterrent, then it must contain some interesting compounds. African bees are not adverse to collecting water from urine, from animal dung, or from making their nest in a tree frequented as a sleeping place for baboons which foul the whole area, yet show no adverse reaction to such powerful odours when foraging.
Another interesting observation was that despite the nest having been vacated about a month ago, the indigenous small hive beetle, Aethina tumida, had not consumed the combs which, although devoid of honey, had plenty of pollen stores and dead brood on which to feed. Several small hive beetles were observed when the owl box was dismantled, but only a single larva was seen (Fig. 5). The small hive beetle belongs to a family of scavengers who nearly always are present in a colony but flourish if the colony should begin to falter through starvation or disease. The small hive beetle is highly adapted to living within a honeybee colony as it is one third the size of a worker bee, has a round, smooth dome and when confronted it merely pulls in its appendages and holds tightly to the substrate. Hence it is able to enter worker cells where it feeds on eggs, pollen and honey. In a strong hive the small hive beetle hides away in crevices where the bees cannot access them. The bees’ response is to confine them in a propolis jail where they are prevented from mating or laying eggs. However, the small hive beetle confined as such is able to solicit food from its captors. This normal reaction where one worker bee may solicit food from another by antennal contact is mimicked by the confined beetle, which is then fed by the misled bee. Should the swarm abscond, the small hive beetle breeds rapidly and their larvae within a short while are able to consume the entire nest and then exit to pupate in the soil in front of the nest. In this way, much like hyenas, they act to control the spread of disease.
The small hive beetle recently found its way to North America and Australia where it has overwhelmed hives because the European races of honeybees on those continents were unfamiliar with it and were unable to contain or expel it. The prolific use of propolis by the African bee may in part be a consequence of containing the small hive beetle where wild nests in cavities may be enveloped in a propolis sheath which denies the beetle places in which to hide (Tribe 2000).
Similarly, wax moth larvae were present only in a small section of the honey-crown (possibly where the lowest titre of diseased spores would be found) (Fig.6) but had not also consumed the brood combs. Were they perhaps also deterred by the presence of the disease?
The above observations are limited to the colonies inspected and it is not known if the above applies to most colonies infected with AFB.
How is AFB spread to wild swarms?
How did this owl-box swarm become infected with AFB? Had they brought the disease with them as a trace of spores when they took up residence and which then took a year to overwhelm the colony? The two hives on the property showed no signs of AFB but will continue to be monitored. Absconding was most definitely as a result of the disease, a behaviour which is consistent with African bee races when faced with adverse conditions (Hepburn & Radloff 1998). The honey containing AFB spores that the absconding bees ingested before departure would be consumed within a few days and in theory they would then have rid themselves of the disease and be free to begin elsewhere again. This is one method that beekeepers use to rid their hives of the disease by shaking the bees into a new hive, burning the infected hive, and starving the bees for about a week to rid them of the spores. Could the owl-box swarm have absconded once before due to the disease but not entirely rid themselves of the disease which slowly built up to overwhelm them?
Natural health of African bees
Beekeepers in southern Africa have adapted their methods to tie in with the ecology of the African bee. The underlying basis of beekeeping in South Africa relies on the trapping of migrating, absconding or reproductive swarms to replenish their ‘stock’. Absconding is ubiquitous in the African races and is induced by dearth, predation or deterioration in nest quality (Hepburn 1993). To those in Europe, Australia or the Americas (the latter two continents having been devoid of honeybees before European colonists arrived) who work with European races of honeybees, this would seem fairly primitive. What is so different in southern Africa is that because they are indigenous, more than 80% of honeybee colonies are still to be found in the wild. Even those that are hived are never really domesticated – they as easily abscond and may again at some stage be re-captured by a beekeeper in a trap-box. However, the great advantage here is that the African bee is still being subjected to natural evolutionary pressures and can be regarded as being extremely healthy genetically. The Varroa destructor mite from Asia which wrought havoc in those countries farming with European honeybees, despite great apprehension initially, was brought under control by the African bee because of two main traits – that of having a shorter life cycle, thus the mite not being in full synchrony with that of its host, and of being more aggressive and physically biting and removing them from the hive. Could we hope that the African bee has the means in its ‘repertoire’ of behavioural traits to neutralise AFB?
Absconding as a defence mechanism?
American Foulbrood appears not necessarily to cause the death of a honeybee colony, which if strong enough after detecting the disease, will abscond before being overwhelmed. If the honey engorged before they absconded is used within a few days and the newly constructed combs are not contaminated with AFB spores, then the colony has a good chance of surviving and ultimately thriving.
Fletcher, D.J.C. 1975-1976. New perspectives in the causes of absconding in the African bee (Apis mellifera adansonii L.) South African Bee Journal I & II. 47(6): 11-14; 48(1): 6-9.
Hepburn, H.R. 1993 Swarming, absconding and migration in southern African bees. South African Bee Journal 65(3): 61-66.
Hepburn, H.R and Radloff, S.E. 1998. Honeybees of Africa: 5. Swarming, migration and absconding. Springer –Verlag, Berlin Heidelberg.
Tribe, G.D. 2000. A migrating swarm of small hive beetles (Aethina tumida Murray). South African Bee Journal 72(3): 121-122.