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Transmission of V. destructor
Robbing by bees is a major source of transmission. As an infected
colony become progressively weaker, its defensive capabilities decline,
and it becomes susceptible to invasion by workers from nearby colonies
(the robbers) seeking its valuable cache of honey. In the process
of removing the honey, robbers become infected with mites and transport
them back to their own colonies. Swarms from infected colonies also
contribute to the local reservoir of mites. These colonies are particularly
susceptible to being robbed because they do not receive any treatment
for mite control. They weaken and die within a year or two and may
be robbed by workers from nearby colonies. Drifting bees, especially
in apiaries where colonies are kept close together, also contribute
to the spread of mites among colonies.
Beekeepers also play a major role in the transmission of mites.
Moving brood among colonies for the purpose of strengthening or
equalizing colonies is a common practice that transmits mites. In
addition, beekeepers often purchase colonies of bees in the spring
to replace winter losses or to increase colony numbers. Some beekeepers
purchase small nucleus colonies, usually called ”nucs,”
from local or regional suppliers. These colonies consist of one
to five combs of bees and brood and usually come with a queen. Others
purchase package bees (2, 3 or 5 pounds of bees, usually with a
queen) from a southern location. An estimated 1 million packages
are shipped throughout the country each year. Each of these practices
spread mites, including various types of pesticide resistant mites.
Migratory beekeeping also plays a role in transmitting mites. Over
a million colonies are moved throughout the country each year as
migratory beekeepers fulfill pollination contracts. After the bloom
is over, colonies are widely dispersed to other locations for honey
production. During the season, some of these colonies may issue
mite-infested swarms into local environments, while others may succumb
to mites and be robbed by local colonies. Each fall, surviving colonies
are returned to a few states in the south where colony numbers are
restored. This brings colonies from many different regions of the
country into close proximity to one another and provides many opportunities
for the transfer of mites among colonies, including various types
of pesticide resistant mites. In the spring, these colonies resume
their migratory routes throughout the country, and the process is
repeated.
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