>Rod Billett from Lexington, South Carolina USA writes
>Could the repeated testing for varroa lead to breeding resistant
>mites???
Actually short one time treatments of a miticide might be a softer push
toward resistance than most might think! It has a distinct advantage in
reducing the duration and thus amount of chemical introduced into the hive.
A debate seems to exist between two scenarios for resistance selection.
One camp prescribes that low constant pressure from an insecticide slowly
selects for resistance in a population. The other maintains that high
pressure from an extremely effective insecticide (>99% mortality) quickly
selects those resistant individuals who reestablish a "new" resistant
population (live to reproduce or die).
The first scenario gently ushers in resistance the second forces the issue
quickly. Most likely the answer is very complex. It may involve a bit of
both but surely selection for resistance includes many variables like the
mites "potential" to develop resistance, dose, duration, weather,
population dynamics, distribution of mites in a hive, apiary location,
drifting--gets very messy to separate out.
That being said, Fluvalinate is a contact insecticide, as such it will only
kill mites that come into direct contact with the chemical. This may
include the mite that boards a bee that had passed the strip, direct
contact with the strip, or contact with comb that in contaminated with
fluvalinate from bees tracking over the strip while moving through the
hive. Mites on adult bees or mites moving within close proximity of the
brood area are exposed when they contact the miticide during treatment.
While mites in capped cells, mites missing contact in the hive, or mites on
bees outside the colony escape treatment. This latter population can be a
large number especially during short treatment intervals.
This is probably too simple of a description but may give an impression of
how treatment affects the colony and mite population.
The 42 day treatment would provide a situation where of an efficient
chemical (>98%) would leave only resistant individuals. By dosing twice a
year the "selection pressure" is for resistance from the surviving
population. However, in between mites come and go through drift,
management activities, moving colonies, etc.
Reuse of Fluvalinate over time along with reuse of wax in frames (I have
frames from 1990 in some hives), allow for slow increase in concentrations
in the comb. This process is assisted by the chemicals oil solubility. It
is more readily absorbed by the wax than by water, thus concentrations can
slowly build up in the wax. Admittedly, the levels may be extremely low
but it is not known what constant contact with low levels may do over time.
Now mind you there are bee operations that treat nearly constantly,
sometimes with multiple chemicals (legal and illegal) which may expedite
resistance. The real moral dilemma exist, especially for the commercial
operator whose livelihood is dependant on bee survival. Use something that
is known to work or await the slow moving process of chemical development
and approval? IT is not my place or intention to place a judgment here.
We as an industry need several consumer safe chemicals that act on
different metabolic foci. Compounds which are safe on paper (safe as
tested by environmental agencies and accepted by environmental
activists)and chemicals which kill mites using entirely different modes of
action. The industry could then shift from one to the another as
resistance appears constantly pressuring the resistant population off base.
This would allow for chemical rotation as a tool to provide protection.
This would be another tool to be used in conjunction with strains bred for
mite tolerance or resistance.
____________________
However, all generalizations are false
---------------------
Mike Griggs
Entomologist/ Support Scientist/Net Administrator FSNL
USDA ARS, U.S. Plant, Soil & Nutrition Lab.
Tower Road, Ithaca, NY 14853
http://www.ppru.cornell.edu/
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