I am most interested in your report of bees leaving the hive because of
Varroa mites.  As I indicated a couple of weeks ago, it appears that this
may have happened to one of my hives in an indoor flight chamber.  Between
Sunday afternoon and early Monday, every bee in a nucleus colony of about
2000 bees left the hive, although they had been in the hive/chamber for
more than two months and had plenty of food in the hive.  Almost all of
the bees died in the flight tube - outside of the hive.  None of the
survivors returned to the hive.
 
This behavior has been reported for tracheal mites.  In this case, we
found no evidence of tracheal mites, but did find a heavy Varroa infestation.
 
Another hive in the same room in an adjacent flight chamber is still doing
fine, although it also has Varroa.
 
One of the more interesting aspects of this event was that the bees
carried??? almost all of the hive debris out with them, presumably before
they died.  Whether the bees died of Varroa, starvation (because of a lack
of food in the flight tunnel - although they had food in the hive and
presumably could have returned to it), or stress of trying to get out of
the flight tube (an impossibility since the tube is not connected to the
outdoors) is unknown.
 
Bill Wilson, USDA, Weslaco, TX  reports anecdotal reports of bees leaving
hives in Texas, possibly because of Varroa.  He thinks that the mites will
not live more than a few days without bee hosts.  We are checking our
equipment to see if that is the case.
 
If anyone has hard evidence that Varroa can cause bees to exit the colony,
I would like to know about it.  Also, any ideas of why they would all
leave at once and then suddenly die???  I would expect them to:
 
1) Leave and fly off
2) Crawl out and die
3) Slowly die and drop to the bottom of the hive where they may be thrown
out by housekeeping bees
 
In our case, they couldn't fly off.  They all died fairly fast, because
the bees had not started to rot (which they do in just a few hours at room
temperature).  The hive debris in the flight tube was a real surprise.
How did it get there????
 
Over the preceeding two months, bees flew from the nucleus hive to feeders
in the flight chamber.  Die off was very low, a few each day.  At nights,
the foragers in the flight tube went back to the hive.  In the morning,
they came out again.  They transferred honey back to the hive and
stored/consumed it in the hive.  Flight activity was somewhat low and
after a couple of weeks, many of the bees elected to walk between the
feeder and the hive rather than fly (but they were certainly able to fly
if released from the tube).  The only thing that we did different just
before they left the hive and died in the tube was to gradually extend the
day-light period from about 10 hours (the daylength here in Montana at
this time of year) to 16 hours.  We were hoping to turn the queen's
egg-laying back on, since our queens pretty much shutdown at this time of
year.
 
Any thoughts will be appreciated.
 
Thanks
 
Jerry Bromenshenk
Univ. MT
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