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Date: | Wed, 30 Oct 2019 15:07:26 +0000 |
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> On Oct 28, 2019, at 19:40, Richard Cryberg <[log in to unmask]> wrote:
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> The best way to avoid development of resistance is to rotate the products used so at least three different biochemical modes of action are involved in killing the pest. For example rotate the use of oxalic acid with amatraz and perhaps thymol (which may kill by the same biochemical pathways as the acids) or an OP. The other best way is to never kill more than about 75% of the existing pest population with a single pesticide at any time. This last one is not very helpful as only killing 75% of the pest population seldom is enough kill to be satisfactory. That 75% can vary from 60% or likely lower up to 90% but there is no way to know the right % until resistance develops and you know a lot about the biochemistry of that particular resistance. So, all you can say specific to varroa is trying for a very high kill rate, like we all try for, is likely to speed up resistance development. And if you do not try for a high kill rate your bees will die. I prefer it when my bees do not die.
Dick: I want to verify that this was not a typo. "Never kill more than about 75% of the existing pest population with a single pesticide at any time" -- to avoid resistance.
This is counter-intuitive (for me at least).
I am going to risk sounding like an idiot here. It seems to me that if you kill 100% of the pest population with a single treatment in one location (let's say one apiary) then there are no survivors from which to develop a resistance for later generations. It also seems to me (intuition only) that resistance occurs when at least one member of the pest population survives the treatment, for whatever reason -- avoidance behavior, unaffected by the mechanism because of a genetic difference from the rest of the population. This member of the pest reproduces, and whatever the reason is for its survival from the treatment, that gets passed on to its offspring and future generations which have a higher likelihood of surviving the same treatment in the future. Assuming that this is correct thinking, then it seems to follow that the fewer pests that survive a treatment application (the higher the kill percentage), the lower the probability of finding survivors who could seed a resistant generation.
I believe that is the reason to rotate treatment mechanisms ... the population of mites and their descendants that are potentially resistant to Miticide #1 who survived a treatment with it are very likely to be killed by Miticide #2, as long as whatever allowed them to survive Miticide #1 will not facilitate their survival of Miticide #2.
My gut keeps telling me that the higher the kill percentage of any treatment, the fewer survivors from which potentially resistant individuals can be found, the lower the likelihood of developing a resistant population.
I realize that this is an incredibly complex subject and I don't expect you to explain it all on a mailing list. Perhaps you can point to some useful reference(s) that can help me / others to understand this better?
--
Rob Jenson, wearing a beekeeper veil whenever possible.
[Email : [log in to unmask]](mailto:[log in to unmask])
https://ferthalangur.spotch.com/beekeeping/
https://www.bee-daddies-apiaries.com
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