By your location, I'll guess that the Queen bumbles are just now emerging
from hibernation and looking for nesting sites.

Mites lack wings. Some mite species evolved dispersion strategies such as
hitching a ride to more mobile insects. This behavior is referred to as
'phoresy'. Likely the mites attached to the bumble were some sort of
phoretic mite that overwintered with the Queen. Phoretic mites use Queen
bumbles as public transport. Some live off of bumble nest debris. The
hitchhikers are making sure the free lunch continues to be available.

Looking through the literature, I found the most common mites on bumbles are
of the genera Parasitellus and Kuzinia. (At least in the north eastern part
of North America). There are at least 20 or so species from these two genera
and others. And, apparently some mites have mites on them. Parasitellus is a
relatively large mite (as mites go) and Kuzinia is much smaller. I read that
Kuzinia attaches to the bumble using an anal suckerplate. Interesting image
that.

You may wonder (I sure did) how the mites avoid inbreeding if they always
stay with Queen daughters raised by the foundress Queen they hitched with
the previous season. If you repeat this scenario many times, it is easy to
see how the mite population would soon be inbred to the extreme. There must
be a way that mites can jump matrilines. As luck would have it (drat, lost
another chance for a grant!) some clever Swiss investigators (Schwarz and
Huck, 1997) demonstrated that phoretic mites (Parasitellus sp.) use flowers
as 'way stations' or perhaps something like a transfer station when one
travels cross country on Via Rail. When the originating Queen forages, they
detach and hide in the flower. Then a distantly related Queen forages the
same flower some time later. A phoretic mite avoiding inbreeding will attach
to this new matriline. Other unrelated mites are gathered along the way or
existing (and unrelated) mites on this new matriline supply the diversity in
the mite gene pool. Poof! In breeding pressure snapped. Got to love
evolution.

I actively encourage bumble bee habitat around my place (The Oligarchy of
Ontario) and have MANY bumbles. But, I have never seen any attached mites on
Queens I've inspected. They may be hiding in the fuzz or body parts. I'll
look a bit harder this weekend and see if I can find any.

It would be interesting to see if Vorroa mites use this method, too. There
is a remarkable amount of genetic variation in the Vorroa jacobsoni species
complex on their native host Apis cerana. Do V. jacobsoni use the 'way
station' method in Asia? Are Vorroa destructor on honeybees as diverse? V.
destructor have preference for drone brood. Are V. destructor mites jumping
matrilines when drones mate? Anyone got a handle on genetic diversity in V.
destructor?

Here's hoping spring is really here and there, too.

Best regards,

Richard Goetze

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