>Thus, an oxalic vaporization in late summer, with 90% efficacy, would be
expected to kill only around 45% of the mites in the hive.  And if repeated
at 7 days (assuming the OA being active for 3 days), for 4 days a
proportion of the emerging mites could reenter cells without being hit by
the acid. Randy 

>I tried 4 treatments at 5 day intervals and monitored the mite drop before and after each successive treatment, attempting to estimate the original and surviving mite population. In several hives the pattern of mite decline was close to what one would predict but in others, usually the strongest hives, mite numbers continued higher than expected and in one hive much higher. I'm pretty certain this was down to fresh mites being brought in from elsewhere. Chris

I closely monitored 13 colonies to see if OAV was a good option for me here between 8/17 and 10/1. Foolishly I treated all my colonies and had no controls. I'm a guy with a high school education and not skilled at science. I'm just trying to keep some bees and make some honey. As with Chris's experience most but not all colonies came from the typical 8 (3%) to 14 (5%) range in 4 treatments at 5 days to 1 to 3 (>1%) That is the good news. 

Two colonies experienced what I assume was invasion. One from 14 on 8/17 to 53 on 9/7 with 2 treatments before 9/7. With 3 more treatments it went to 32,8, and finally 3. Another colony went from 4 on 9/26 to 65 on 10/1 with 2 treatment in between. It got the old blue towel treatment to put out the fire and was at 5 on 10/6. These were each in different yards and randomly selected for test so if 15% of colonies are getting potentially deadly late season invasions that is scary.

One did not seem to react. At 11 pre to 5 after 1, 3 round treatment to 8 after 2nd  4 round treatment. It also got a blue towel and was 1 on 10/1. How ironic if we see OA resistance before we loose amatraz. 

I greatly admire and envy Randy's ability to monitor 1000 colonies but as a one man band and well into my dotage it just ain't in the cards for me. I do not think I was getting close to 90% of the phoretic mites with each application and as Randy has expertly shown 50% kill will only mark time at best. I do believe that as a one time no brood winter treatment it is a no brainer. My home and highest yard where brood rearing is largely done by mid Sept. did the best with all colonies below 1% after 3 5day treatments so brood is the key I believe. As a treatment early enough to give a good 6 weeks to raise winter bees after the honey harvest I am not yet convinced.

Paul Hosticka
Dayton WA

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