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THE ESSEX NATURALIST
Figure 2. Scheme showing history of Parasitus bomborum during a full
year. Left sector: metamorphosis of mite. Right sector: methods of
dispersal (some hypothetical) of deutonymph—stage which travels on
bees. Winter: late September to late May. Both: period when mites
are in nest and also undergoing dispersal by Psithyrus.
Once on the body of the bumblebee the mites are exceedingly
difficult to remove, and cling tenaciously to their host. At the
end of the season large numbers of mites may be seen clinging to
some queens and drones. Step records up to 100 mites on a single
queen but I have never observed more than half this number.
Towards late September the mites must either die or transfer
from the drones to queens, because the drones die usually in early
October. This transfer may take place during copulation. The
drones and queens sometimes copulate in the nest. The drones
find a mate by some chemosensory means as no light normally
enters the underground nest. This infers that the mites may also
distinguish between drones and queens by similar chemosensory
means. I have not observed copulation of infected bumblebees
and know of no-one who has, so the transference of mites from