Managing Varroa Mites
in Honey Bee Colonies
The varroa mite ( Varroa destructor) is the most serious pest of honey bee colonies
worldwide. This parasite was first detected in North Carolina in 1990, having been
introduced to the U. S. just three years earlier. Virtually all feral ( or “ wild”) honey
bee colonies have been wiped out by these mites, and beekeepers continue to strug-gle
with varroa infestations in their hives. In North Carolina alone, the number of
managed beehives has dropped by an estimated 44 percent since the invasion of the
mites. It is vital, therefore, to understand the varroa mite and the options available
for its control.
Mite Biology
The varroa mite is an external parasite that
attacks both adult bees and the developing
honey bee larvae. The adult mites have a
flattened oval shape, are reddish- brown
in color, and are about 0.06 inches wide,
about the size of the head of a pin ( Fig-ure
1). The mated female mite enters the
cell of a developing bee larva and lays as
many as six eggs. The developing mites
feed on the bee pupa and, depending on
the number of mites, may kill it, cause it
to be deformed, or have no visible effect.
While the male mite dies in the cell, the
adult daughter mites climb onto an adult
worker bee and feed on its hemolymph ( a
fluid known as “ bee blood”). The female
mite can then repeat the cycle by enter-ing
cells of other developing larvae. Mites
prefer drone larvae over worker larvae, but
they will infest worker larvae and eventu-ally
kill the colony if preventive measures
are not taken.
The mites can also harm the bees in-directly.
In addition to the obvious effects
of mites feeding on developing and adult
bees, the mites can also serve as transmit-ters
of several viruses that can kill bees.
These secondary infections are facilitat-ed
when the mites compromise the bees’
immune systems. They can cause a
condition known as parasitic mite syn-drome
( PMS), which can kill colonies
within months of infection.