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Life Cycle of V. destructor
The life cycle of the mite can be divided into phoretic and reproductive
phases. The reproductive phase begins when a mature female leaves
her adult host, enters a brood cell containing a worker or drone
larva shortly before it is capped, and sequesters herself in the
bottom of the cell. Soon, the cell is capped; and shortly thereafter,
the immature bee enters the pupal stage. Egg-laying commences about
60 hours after a cell is capped, and both mother and offspring feed
on the host’s hemolymph. Mature offspring mate within the
cell, but only mature females survive outside the cell.
The number of offspring that reach maturity is positively correlated
with the length of the host’s capped stage, which is greatest
for drones, intermediate for workers, and shortest for queens. Mites
that reproduce on drone brood average 2.2 to 2.6 female offspring
per host, while those reproducing on worker brood average 1.3 to
1.4 female offspring per host. Mites cannot reproduce on queen brood
due to its short capped period. Not surprisingly, mites are found
more often on drone brood than worker brood, with average differences
between 5- and 12-fold. Mites are only rarely found on queen brood.
The phoretic phase begins when the host emerges from its cell as
an adult bee. The mature female mite may leave the cell with its
adult host, or it may walk out of the cell and acquire an adult
host. Mites remain on an adult host for a few days or weeks before
entering a brood cell for the next round of reproduction. Mites
are found twice as often on bees in the brood nest as on bees in
the honey supers, and 10 times as often on brood nest bees as on
foragers.
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