Hi Everyone,
Just one other point that needs to be considered on this issue.

[log in to unmask] wrote in part:

" put simply when we use any control we kill most of the
mites suseptable to the control, there is always a genetic variation in  a
population and amongst that variation there will be a small number able to
survive that breed more survivors for that control method. so if you cull
drone comb your selecting for mites that breed in worker brood,if you use
apistan your selecting for apistan resistant mites ect ect ect any
resistance to any treatment depends on breeding generations and the number
treatments used and the variation between unrelated treatment in use."

Well put on the mechanisms involved in resistance development.  It is merely a matter of selection.  There is another factor involved that largely determines the speed at which such resistance appears.  That is the selection pressure or to put it another way the effectiveness of the treatment.  The more effective the treatment ( the greater the selection rate ) the faster resistance will be selected for.  So it follows that the less effective treatments will select for resistance more slowly.  This may be why some treatments have been used for long periods without resistance appearing such as formic acid treatments in Europe.  Those treatments that accumulate in wax greatly extend the time of exposure to the treatment which of course results in stronger selection for resistance.

This leads to one other area of comment.  Sub-lethel levels of treatment materials do not lead to resistance.  Think about that.  If the material is present at levels that do not actually kill mites there is no selection for resistant mites.  The greater the kill rate the faster the selection for resistance since only the resistant members of the population survive to reproduce.  Again application of treatments at sub-lethel rates do not result in selection for resistance.  Look at it another way: misue of a treatment by leaving it in the hive longer that label will only select for resistance if the treatment strips continue to kill mites for the entire time they are in the hive if they "wear out" or the active material falls below treatment levels there is no selection for resistance.  Not condoning in any way disregarding the label but from a resistance standpoint overapplication is a much stronger selection for resistance than underapplication.

FWIW

blane


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Blane White
MN Dept of Agriculture
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