There are a large number of hive management practices that contribute to the spread of AFB.
- Amount of brood shifted between hives
- Making of splits, tops and nucs
- Exchange of wet or dry supers between hives
- Use of feed honey or pollen
- Movement of hives from one location to another, and the splitting up of apiaries
- Speed with which diseased hives are destroyed
- Methods used to sterilise equipment
- Misdiagnosing AFB or not wearing reading glasses (if required).
This list is not complete, but it does provide an idea of the complexity involved. The significance of each management practice depends on the overall disease levels in the beekeeping outfit. For instance, if a management practice increases the disease incidence five-fold from 0.5% to 2.5% that might be painful. However, if the same management practice produces the same five-fold increase, and the starting level is 5%, the resulting 25% incidence would be disastrous.
Examples of risk
Any swapping of equipment between colonies carries a risk with it. However, the way the equipment is exchanged affects the size of the risk. As a first example, three frames of bees and brood are removed from one hive and papered on to a second hive to increase its strength. At worst, taking it from an unrecognised AFB hive will create one more AFB hive. Fortunately, most beekeeping activities fit this model, so the activity only doubles the number of AFB hives.
The second example is where an activity more than doubles the number of AFB hives. A good example of this is extracted honey supers. While the infectivity of “wets” has not been properly determined, it is safe to assume that it is less than exchanging frames of brood. For the sake of discussion let us say that the extracted honey supers from an undiagnosed AFB hive infect 75% of the hives they are placed on. This being the case the bigger the honey crop and the greater the number of supers used, the greater the risk from the AFB hive. Two extracted honey supers from an AFB hive will infect 1.5 other colonies and four supers will infect three other hives, if the supers are placed on different hives.
The situation gets worse when the components of an AFB hive are spread even further. For example, supers of honey are often kept to feed nucleus colony that are over wintering. If the supers are taken from an AFB hive, assuming a 75% chance of a frame infecting a colony, then an AFB hive has the potential to create 13.5 new AFB hives.
Feeding extracted honey or pollen can be even more disastrous. There are a number of cases where beekeepers have fed extracted honey or pollen to a large number of other colonies. One of the hives supplying the honey or pollen had AFB with the result that one hive was turned into 20 or 30 AFB hives.
Another example is where a beekeeper has been producing queens and has found out that the starter being used has AFB. Several hundred queen cells may have been started and placed in several hundred hives.
Assess risk before you begin
A good principle is therefore to assess the risk of removing something from a hive to place it into another. If it is only being placed in a single hive then be careful. At least carry out a complete brood check. However, if what you remove is going to be placed in more colonies, you need to be very sure that the source of the material doesn’t have AFB.
When deciding on a beekeeping practice, assess how many hives could become infected if things go wrong.
Unchecked, the AFB incidence in an outfit can increase exponentially. Assuming each AFB hive creates a new AFB hive each year and none is found then the incidence will double each year (Fig. 62). A doubling of AFB hives each year will increase AFB incidence from 1% to 60% in seven years. If each AFB hive produces two AFB hives each year than the incidence will increase from 1% to 60% in four years.
Figure 62: Increase in the percentage of AFB hives with 0.5, 1 and 2 additional AFB hives infected
by the hives present the previous year
These rapid increases are the reason beekeepers are sometimes caught unaware with a major problem. If you have only a 0.5% incidence, the worst that you can expect next year is 1% or 2% if things go wrong, as there are not that many AFB hives available to infect other colonies. However, if you have a 5% AFB incidence, you are sitting on a potential time bomb. Get it wrong and you may have 20% next year.