Nick, in the Fingerlakes, says "There were lots of mites in
July/August which was 1-2 months earlier than normal."  He goes on to ask
"Does anyone on the list have any ideas on this?"
 
I have never heard of any correlation between bees under stress (drought
conditions) and large numbers of mites.  In fact, such is not logical as
mites require large amounts of larvae to increase their population.
 
However, large numbers of mites in July/August is a common condition and
many hives are lost to this every year.
 
I first noticed this around 5-6 years ago.  Often my best hive or hives
would collapse in August, no bees, and loaded with honey and pollen.  While
now I know how to look for signs this might happen, and take action, I still
lost one hive to this in 1998 and a commercial beekeeper nearby had severe
August losses.
 
Nick Calderone, from Cornell, opened my eyes to what is going on.  Nick
pointed out that mites need a lot of larvae to multiply, and that the best
hives always have a lot of larvae (which is why they are the best hives).
Nick said "your strongest hives will always have the largest populations of
varroa".  Make sense, so far.  However, as the strongest hives have more
bees to carry the varroa, why should they necessarily collapse?  This has to
do with their biology, as well as the natural cycle of the hive.
 
Varroa, as everyone knows, prefer drone larvae.  However, in July/August the
bees are raising relatively few drones so as the mite population increases
and the drone larvae decrease, the mites start to attack worker larvae.
Once they infect a large percent of worker larvae, the hive is doomed.
 
The control, as pointed out by Nick, starts with inspection of worker larvae
in strong hives.  Uncap and pull out of cells, just as one does for drone
larvae.  If mites are present in reasonably large numbers on worker larvae
(personally, if I see mites on 25% of worker larvae I consider it "large
numbers"), take the supers off the hive, and put in strips for one week.
Then pull strips and put supers back on.
 
In that week, perhaps 50% of the mites will have been killed...enough to
reduce the mite population to  below lethal levels.  While a prime week's
collection of nectar will have been lost, it is better than losing the
entire hive.
 
Hope this helps,
Lloyd
[log in to unmask]
Owner, Ross Rounds(tm)  the finest in comb honey production.