A STUDY OF THE MITE PARASITUS BOMBORUM 287
drones to queens during copulation must remain hypothetical.
After copulation the queens hibernate with the mites on them.
On two occasions I have found queens (Bombus lapidarius) hiber-
nating in holes approximately four inches below the ground
surface. Each queen was infested by approximately twenty mites.
It is interesting to note that there is a tendency for the mites
to attach themselves in places on the bee's body where they
appear least likely to be blown off. They position themselves on
the bee's body in the joints and the immediate vicinity of head,
thorax and abdomen (see Figure 1E).
One of the many interesting points that have arisen from this
study of mites and bumblebees is whether or not the mite is a
disadvantage to the bee. From my observations I formulated the
following hypothesis: that within certain limits the mite popula-
tion may be an advantage to the bee colony, but beyond these
limits it may become a disadvantage. It would be a disadvantage
to the colony if the bees had to forage not only for themselves but
for a large mite population. Below the optimum population the
mites would eat a negligible amount of food and by their scaveng-
ing aid cleanliness among the members of the colony, for bees
exhibit a 'depressed' behaviour pattern when dirty. It was
observed that a bumblebee, on returning to the nest, having
fallen into the 'honeypot' feeder and become covered in sugar
solution, immediately attracted a number of mites onto its body.
Concerning the dispersal of the mite there are a number of
insects which, at some time in their lives, by coming into contact
with the bumblebees may aid the dispersal of the mites. One
such is the parasitic bumblebee Psithyrus, which is known to take
advantage of the bumblebee's nest in the same way as the cuckoo
does of birds. It is, therefore, not unreasonable to suppose that
the mites of an infested nest come into contact with the Psithyrus
when she is laying her eggs. The mites may attach themselves
to Psithyrus and then drop off later in an uninfested nest.
Prima facie an overall conclusion would be inappropriate due
to the inadequacy of observations. An approximate picture has
been attained of the deutonymph stage but observations have to
be made on the larval stage (which I have not yet observed), and
many more on the protonymph stage and the adult. The relation-
ships between the bumblebee and the mite have still to be proved,
and a possible moderating relationship as the mite develops should
not be overlooked.
I would like to acknowledge the help and encouragement of
A. Darlington and J. B. Dobinson in the work recorded in this
paper, and the help of L. Milne and A. R. D. Stebbing in its
presentation.
References
Free, J. B. and Butler, C. G. (1959). Bumblebees. Collins, London.
Lee, D. C. (27 November 1963). Personal correspondence.
Step, E. (1932). Bees, Wasps, Ants and allied orders of the British Isles,
Warne, London,