220.127.116.11. Obtaining mite free colonies
Mite free colonies can be obtained from varroa free areas. These colonies will also be residue free since acaricides are not used. Obtaining such colonies is usually not possible so the varroa population of the experimental colonies needs to be removed using a highly effective control method adapted to the region in which the study takes place. The occurrence of resistant populations needs to be taken into account when choosing an acaricide for this purpose (see section 3.6.3. ‘Bioassays to quantify the susceptibility of the varroa mite to acaricides’ for methods to test for resistance). The efficacy of the treatment should be checked, as well as putative re-infestations from neighbouring apiaries (Greatti et al., 1992).
Depending on the experiment planned, residues left behind by such treatment could bias the results by provoking delayed mortalities of mites. In such cases, residue free oxalic acid treatment can be used on swarms. No capped brood or frames with L5 larvae (see the section ‘Obtaining adults and brood of known age’ of the BEEBOOK paper on miscellaneous methods (Human et al., 2013)) should be carried to the experimental hives in order not to bring in mites. Formic acid treatment can also be used on entire colonies with brood since the acid affects mites under the cell capping (Adelt and Kimmich, 1986; Koeniger et al., 1987; Fries, 1991; Calis et al., 1998). However, these two methods are only 95 % efficient on average, which can influence the planed experiment. Oxalic and formic acid based products are available on the market and should be used as per manufacturer recommendations.
In such experiment, a control group of colonies treated continuously might be necessary. Such colonies need be separated from the experimental group since drifting and robbing bees could contaminate the test apiary (especially and mostly with synthetic acaricides; Allsopp 2006). For the same reason, the control and experimental apiary need be separated by the same distance (~2km) from neighbouring uncontrolled apiaries. However, a compromise distance between control and experimental apiaries needs be found so that both are still subjected to equivalent environmental conditions.