Screening of substances for their effect on Varroa jacobsoni: attractiveness, repellency, toxicity and masking effects of ethereal oils
Bernhard Kraus; Nikolaus Koeniger; Stefan Fuchs
Tests were developed to enable the screening of substances for effect on the orientation of the honey bee parasite Varroa jacobsoni. Mites collected from young bees in an Apis mellifera carnica colony were used in the tests, which employed wax tubes incorporating the test substances. During a test, mites could remain in a tube containing a test substance or move from it into a tube of pure wax without the test substance. Twenty-two out of 32 tested ethereal oils had a clear repellent effect on the mites. Oil of clove and oil of cinnamon proved to be the only ones with a clear attractant effect on the mites. The most pronounced repellent effect was caused by oil of citronella. Oil of marjoram was clearly capable of masking odours. In toxicity tests, most of the tested oils caused a distinct increase in mortality of mites which were exposed to them incorporated in wax at a concentration of 0.1 %. The other tested ethereal oils caused an increase in mite mortality at a concentration of 1.0% or more. The repellents oil of marjoram and oil of citronella, and the attractant oil of clove, were mixed into the comb foundation wax of test colonies. The infestation rates of I. Jacobsoni in capped brood cells was clearly higher in colonies with oil of clove foundation than in control colonies with normal foundation. The infestation rate was only slightly lower in colonies with oil of citronella, but clearly lower in colonies with oil of marjoram foundation, than in control colonies. This result indicates that a treatment with oil of marjoram might be a way to decrease the population growth of this parasite.