I have been through about 150 hives this past week, and have some
observations to make about the progress of varroa. First a little background:
We found the first varroa mites about four years ago. Since then it has
spread slowly, and has been readily controlled, and not a serioius problem.
Last year was the first year the entire outfit was treated, all during the
winter, mostly during late winter.
When we were pulling strips in the spring we found three hives without
strips :< ( ...Must have been my help - couldn't have been me! :< ). These
three hives were in the last stages of crashing, with few adults. Sealed
brood was hatching, which were undersized, often with very tiny or almost
absent abdomens, and some with no wings. Many of these emerged, crawled
around a few minutes and died. I have some video of this event.
Early this fall, checks showed some varroa mites in some colonies, but my
impression was that they were at a low level. But this past week, we saw some
that were crashing.
I also assisted another beekeeper in a fall check of his 40 hives. He had
kept strips on his bees all summer (He is a grower, not interested in honey.)
Most had Apistan, but there were 6 with the amitraz strips, which he did not
know had been recalled. We also found one with no strips. These seven were
all in bad shape, with heavy mite infestations.
The idea has been tossed around that the seasonal end of drone rearing is
a time when hives are very vulnerable, as the mites then switch to worker
brood. This is borne out by my observations this past week. I have rarely
seen any mites on worker larvae or pupae throughout the summer. The colonies
that were crashing, had mites much of the worker brood, and I saw a few with
five or six per each.
When mites first arrived, we were told that one treatment per year would
be sufficient. At this point, I think this is questionable, at least in the
south. The first buildup was very slow, but the rebound after treatment was
much faster, either because the treatment missed quite a few, or because they
had a source of reinfestation. (I suspect the latter is more the case.)
I also had caught three swarms this spring that I held separate because
they came from areas where no bees have been kept for several years, and I
hoped to find resistance to varroa. I fed them, but did not treat for mites.
Two died of mite infestations during the summer. The third is now dying of
mites. So these had no resistance; they just had not yet been infested. I'll
keep trying on this score, and I think all of us should do this, if we can.
Some management conclusions:
1. The hives with varroa problems could not be distinguished by a weight
test. Most of them had adequate stores. The difference could only be seen
inside the hive, and by close inspection of brood.
2. Amitraz, even with all its other problems, apparently is just not very
effective for varroa.
3. Beekeepers need to be especially alert at the end of the season, when bees
stop raising drones. Scratch open some worker brood and see if there are any
mites present on workers. They also can be readily spotted on adults, if you
hold the frame in sunlight and train your eye to spot the shiny brown dots.
4. We are in a very vulnerable situation, with only one material to treat for
these mites. If resistance to fluvalinate develops, what then?
We need an alternate, so we can switch back and forth, to reduce the chances
of development of resistance.
PS#1 We did find a few feather-light hives. In each case I found a few cells
of chalkbrood - a disease that I think is underrated. We eliminated these
hives; I do not want to nurse them through winter only to have them provide
drones for next years breeding. Had we found them earlier, we would have
requeened.
PS#2 With all the attention on mites, we must not lapse on foulbrood
control. I found four in the forty kept by the farmer-beekeeper.
PS#3 I might not be around much for the next couple weeks. We'd better get
to treating the rest of the outfit - fast. I don't think we can afford to
wait until late winter like last year.
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