Bees drifting between hives
Bees drift from one hive to another, particularly when hives are set out in straight lines, when they are all painted the same colour, or when the entrances of hives are placed close together.
The drifting of bees between hives is often mentioned as a major factor in the spread of AFB. Beekeepers cite examples where if one hive develops AFB, the one next to it will also develop AFB. However, there are many more examples where this does not happen, so coincidence cannot be ruled out.
The hive next to a hive infected with AFB will usually be the next one worked by the beekeeper, and if hive parts are intentionally or inadvertently moved between hives, they are most likely to end up in the hive next to the one with AFB. It is therefore very difficult to be sure whether a hive developed AFB through drift or from other means.
Experimentation undertaken to understand drifting as a factor in the spread of AFB
Trials have been conducted to determine whether bees drifting from hives with low level AFB infections (less than 50 larvae/pupae exhibiting disease symptoms) are likely to spread AFB. Hives with low-level infections are the kind that a beekeeper is most likely to miss.
A total of 24 pairs of hives were set up, each pair consisting of one hive with a light AFB infection and one uninfected hive. The hives in each pair were facing the same way and positioned as close together as possible in order to maximise the level of drift.
When the level of drift between the hives was checked, it was estimated that the equivalent of 50% of the bees had swapped hives over a 20-day period. However, this may have been because of a smaller number of bees moving backwards and forwards between hives several times, rather than 50% of the bees swapping hives.
The pairs of hives were together for a total time of seven years (an average of 103 days for each pair). Only two of the non-infected control hives developed AFB. Both hives developed AFB at the same time that 12 other hives in two apiaries involved in another experiment close by also developed AFB. It is possible that the infection in these two non-infected colonies could have been because of robbing.
What is obvious, however, is that since only 8% of the control hives developed AFB, bees drifting from hives with light AFB infections cannot be considered to be a major factor in the spread of AFB. Whether the same can be said for drift from colonies with heavy infections is unknown.
Even if drift is not an important means of spread of AFB, care should still be taken to reduce it to a minimum, since excessive drifting can affect honey production.
Reducing the likelihood of drift
Three simple methods are effective in reducing drifting between hives.
- The use of irregular or non-repetitive layouts (patterns) of hives, and situating hives so they face different directions
- The use of different coloured supers
- The use of orientation marks near hives.
Since bees drifting between hives can spread AFB, beekeeping practices that minimise drift should be used.