Control AFB by understanding how it spreads
To be able to control the spread of AFB, it is important to understand how the disease is transferred between colonies. A number of possible means of spread have been suggested by beekeepers. These include:
Extracted honey supers
- Transfer of brood frames and honey frames
- Empty used comb
- Other contaminated hive parts
- Queens and package bees
- Bees wax foundation
- Varroa control strips
- Beekeeping equipment (gloves, hive tools, honey extractors, etc.)
- Flowers and the ground in front of hives
- Feeding contaminated honey and pollen
In discussing the possible ways that colonies can become infected with AFB, it is important to remember that AFB infections do not occur because a single bacterial spore finds its way into a colony.
In controlled experiments it has been shown that several million spores need to be fed to a honey bee colony in either sugar syrup or honey to infect one or more larvae.
Obviously, large numbers of spores are usually required to initiate an AFB infection. So probably the best way to assess the importance of the various means of spread is to compare their relative ability to transfer large numbers of spores from one colony to another.
Common causes of AFB spread
Unfortunately, by far the most common causes of AFB spread are beekeeping management practices. The most significant of these are:
- The movement of extracted honey supers between hives (often a year later)
- Transferring brood or honey frames between colonies.
Most of the other causes beekeepers normally blame for the spread of AFB turn out not to be as significant or widespread as beekeeping management practices.
Robbing can be an important cause, but when it leads to an AFB infection, it is usually the result of inadequate levels of beehive inspection (i.e. poor beekeeping management practice). Robbing of feral colonies is not a major source of AFB, at least in most situations and areas of New Zealand.
Although the drift of bees from AFB hives to healthy hives can spread AFB, particularly if the infection is advanced, it is probably not an important factor in the transmission of AFB from lightly infected colonies.
Such things as hive tools, smokers and gloves, as well as the soil in front of hives, foundation, and queen bees, are of little consequence as sources of spread of the disease.
Possible means of spread of AFB are discussed in greater detail in the sections that follow.