188.8.131.52.6.1. Assessment of efficacy
1. Count dead mites on the bottom boards at regular intervals before, during and after treatment.
The primary variable is mite mortality. During the treatment period dead mite counts should be carried out every 1-2 days given the high mortality expected. Pre- and post-treatment counts should be made 1-2 times per week depending on amount of mites falling, see section 4.2.4. ‘Natural mite fall’ and 4.2.5. ‘Sub-sampling mite fall’. This allows the verification of efficacy since mite drop should peak during the treatment period.
2. Determine the amount of mites surviving the treatment with the product under investigation using a follow-up treatment with a chemically unrelated substance with >95 % documented efficacy.
Follow-up treatment should be carried out in tested and control groups at the same time. This follow-up treatment should take place shortly after treatment with the test product, in order to keep the re-infestation level (and therefore the biasing of results) low when test apiaries and groups are not isolated by enough distance from neighbouring apiaries or hives. However, it is necessary to wait until mite drop returned to pre-treatment level in order to measure the full effect of the treatment and dissipation of the delayed mite mortality. This period is at least 14 days if the product kills mites in the cells or not. It is only after worker emergence that these mites will be released and fall on the bottom board or that they will get into contact with the product if the latter did not penetrate into the cell.
3. Count dead mites every 1-2 days in the week after follow-up treatment and 1-2 per week until mite drop returns to pre-treatment values.
4. Calculate treatment efficacy as follows:
% mite reduction = (number of mites in test group killed by treatment x 100) / (number of mites in test group killed by treatment + number of mites killed in test group by follow-up treatment)
Do not use data from colonies with abnormally high bee mortality in the efficacy evaluation.
5. Compare mite fall after treatment with untreated control to verify that the fall measured was not a natural phenomenon.