In 1999, an isolated honey bee population of 150 colonies was established on
the southern tip of Gotland. The colonies came from a variety of locations
around Sweden with different genetic backgrounds and were equally infested
with an average of 50 Varroa mites in each colony. These colonies were to be
part of a selection experiment to evaluate if the mites would eradicate an
isolated population of bee colonies under natural Nordic conditions. For this
purpose, the colonies were unmanaged, allowed to swarm freely and did not
receive any mite control treatments. The experiment was called the “Bond
Project, Live and Let Die” as some colonies would live and some would be let
to die. The bees in this project have thus become known as the ‘Bond Bees’. A
central hypothesis to the Bond Project was that beekeeping management
strategies inhibited the natural development of mite resistance in two main
ways:
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1. Swarm prevention inhibits colony level vertical transmission pathways,
increasing the emphasis on horizontal transmission pathways, which
may result in the evolution of more virulent mites.
2. Mite population control treatments remove the selective pressure of
heavy mite infestation that would be required for natural selection to
shape host adaptations towards tolerance and resistance.
The Bond Bees have been continuously monitored for swarming, winter losses,
mite infestation rates in the fall, and bee population size in the spring since the
beginning of the project (Fries et al., 2003, 2006). Many of the bee colonies
swarmed in the first two years of this project, but by the third year the
increased mite infestation had weakened the colonies and the swarming rate
decreased significantly (Fries et al., 2003).
Within the first three years more than 80 % of the colonies in this project
died (from 150 to 21 by 2002) due to the rapid build up of mite infestations
rates well over the winter mortality threshold (Fries et al., 2003, 2006).
Nevertheless, more than ten years post mite introduction, a small number of
colonies still remain that have survived without mite control and have
established themselves as a hybrid sub-population (Paper I).
After the initial losses, the mite infestations rates in the fall decreased,
winter mortality decreased and the incidence of swarming increased again as
colonies were again strong enough to do so (Fries et al., 2006). Although
swarming reduced the mite infestation in the mother colonies of this
population, it was not enough to prevent the development of high mite levels in
the fall. Therefore, it was concluded that the ability to swarm probably does not
limit the mite population growth enough to fully explain the survival of the
Bond Bees (Fries et al., 2003).
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