188.8.131.52.3. Data analysis
For each Petri dish, a score is calculated summing the number of mites that were found on the bees during the six observations. This ﬁgure can vary between 0 and 6 and is representative of the time the varroa mite spends on the bees. The score can thus be considered as a measure of the preference of the mite for the stimulus under testing. Data from all the replicates are organized in a matrix with as many rows as the number of mites used in the bioassay, and 2 columns containing the scores of the 2 stimuli to be compared. As the variables under study have an unknown distribution, the scores of different stimuli in a data set are compared by a sample randomization test (Sokal and Rohlf, 1995; Manly, 1997). The randomization distribution should be re-sampled a sufficient number of time (e.g. 106 times).
Active chemicals identified by means of laboratory bioassays can be tested in the field. For methodologies see section 4.5.4. ‘Testing varroacides in the field’. This guideline describes the testing of acaricidal effects. However, it can also be used when using substances that do not kill mites, but disturb their orientation and reproduction. The effect expected is not mite death, but a reduction in mite population size in the colony which can also be detected with this method.