******************************************
Blane White
MN Dept of Agriculture
[log in to unmask]

>>> [log in to unmask] 06/22/00 12:49AM >>>
"bryan Clements" <[log in to unmask]> wrote:
>I was recently in a yard of bees that had tested positive. At the first test
>the worst board  had 50 mites and every other board had 5 or 6 mites. 50% of
>the yard had sticky boards. We visited the yard two weeks later and
>inspected 75% of the hives. We used the brood fork and did 6 digs into brood
>in each hive. Made a great mess. We looked and looked everywhere and did not
>find one mite. There was no drone brood present.
>To me it appeared as if the sticky board test was very accurate and that
>finding mites in a yard with light infestation was impossible with the eye,
>even when digging out brood.

Robt Mann
consultant ecologist
P O Box 28878   Remuera, Auckland 1005, New Zealand
                (9) 524 2949

Replied in part:

"The simplest hypothesis would be to credit the
Apistan with having achieved this, but I don't find this plausible.


        The complete absence of drone brood is itself interesting.
        Is there some suggestion that varroa cannot breed with comparable
efficiency in worker brood?

        The insensitivity, more accurately called a high threshold, of the
Apistan/sticky board test is beyond dispute, isn't it?  Of course, one has
to say 'compared with what'.
        One can imagine a hive that has many adult mites but for some
unknown reason has few or no mites in the brood.  A colony in that
condition will register positive on the strip/board test.  But the greater
fear has been scoring negative on that test while many mites are breeding
up but not yet capable of falling onto the sheet (or of being poisoned by
the Apistan) because they're sealed in capped brood.  In that condition,
the hive will have a high threshold or severe insensitivity on the
strip/board test.
        I have been assuming this latter is the more common situation.  Any
expert correction?"

Hi Robt and others,

You are starting to get into the "interesting" aspects of varroa biology.  First even 50 mites on a sticky board does not mean there is a very great mite population in the colony.  How many bees were in the colonies?  How many brood cells were examined?  If there were 30,000 adult bees in the colony and you dropped 50 mites that is only a infestation rate of 0.17 % not a high infestation at all.  If you opened 50 cells of brood you would likely miss the mites.  The rest of the colonies tested about 10 times fewer mites so how likely are you to find mites in a relatively small sample of brood?

Many factors interplay to result in the mite drop on this test.  One is that at the time when drone rearing stops the number of mites on the adult bees increases markedly and you can get seemingly high test results without high mite populations.  Also under these conditions where a larger than expected portion of the mite population is on the adult bees you will get very quick knockdown with apistan.  Again 50 mites is not a very high infestation.  I have seen literally 1000's of mites on a 24 hour apistan sticky board test from a colony with no visible damage due to the mites.  When you treat with apistan or other similar products that are effective a very large portion of the total mite drop occurs in the first few days of treatment.  At times this test is rather sensitive but as you cautioned not always.  You are correct in assuming that some even many of the yards that tested negative actually have low level infestations of varroa that will become apparent only with time.

It also is not unusual to find seemingly great differences in infestation levels from colony to colony in a yard and this is more likely when mite numbers are low as in the case here.

There is much we don't understand about varroa and the relationship between the mites and their host honey bees.

blane