Bioassays for volatile substances

1. Dissolve the active ingredient (e.g. thymol) in asuitable solvent (e.g. diethyl ether) at the concentration 0.5 g/ml.

2. Treat a circular area (diameter=6 cm) of the inner side of the lid of a glass Petri dish (diameter=14 cm) with 250 µl of the solution.

3. Let the solvent evaporate.

4. Place 10 to 15 varroa mites on the bottom of the Petri dish and keep different groups inside the closed container for 0, 15, 30, 45, 90, 135 min at room temperature.

Mites of the same origin as for the bioassay for susceptibility to contact substances are used (see section ‘Bioassays for contact substances’).

5. After each interval, transfer the group into small Petri dishes (Æ=6 cm) with one bee larva for every five mites.

6. Place in an incubator at 34.5 °C and 60-70% RH.

7. Monitor mite survival at 48 hours.