188.8.131.52. Cell invasion
In the case of the compounds affecting cell invasion (ether attractants or repellents), field testing involves treating brood cells with the chemical under study and evaluating the number of mites that entered the cell after it has been sealed.
1. Dissolve the compound to be tested in 1 µl of de-ionised water or other appropriate solvent.
The dose used for the field bioassay is normally the most active in the laboratory bioassay. Beware that the solvent might dissolve the wax of the cell walls.
2. Select a highly infested colony.
3. Identify cells containing L5 larvae (see the section on obtaining brood and adults of known age in the BEEBOOK paper on miscellaneous methods (Human et al., 2013).
4. Apply the solution to these cells' walls with a 10 µl Hamilton syringe.
5. Treat an equal number of cells with 1 µl of water or solvent as a control.
6. Mark the position of the cells on a transparent sheet for subsequent tracking.
7. Open the sealed cells 18 h after treatment.
8. Inspect the cells for the presence of mites and count mites.
The proportion of treated and control cells that were infested are compared using the Mantel-Haenszel method after testing the homogeneity in the odds ratios of the replicated 2 × 2 tables. Any test that is suitable for comparing proportions could be used instead. However, if there are more replicates, using a certain number of cell each time, it is recommended to use a test that allows the analysis of strata. The number of mites in treated and control brood cells, in the hive bioassay, can be compared by a stratified sampled randomization test.