Krisztina has been conducting research of Varroa destructor mite size variability within the United States which led her to investigate biotic, abiotic and genetic factors behind this phenomenon.
This research became a high priority when a small mite was discovered in the U.S. that appeared to be Varroa jacobsoni, the descendant of a shared ancestor of V. destructor that only infests the Asian honey bee (Apis cerana) in Asia. Molecularly it was determined to be V. destructor but it raised the substantive question of what are the selecting pressures for smaller mites in the US that may have consequences for bee management.
Beekeepers are having difficulty controlling Varroa mites, as products traditionally used by beekeepers are failing to control mites adequately. One of the most used synthetic acaricides is a formamidine: Amitraz the active ingredient in ApiVar®. This miticide treatment showed great efficiency in the past but recently has not delivered the expected mite removal. To test whether abiotic factors such as miticide exposure had different affects based on the size of a mite and if they had an effects on miticide efficacy, Krisztina tested the hypotheses: Are larger mites better able to tolerate prolonged miticide exposure than smaller ones? She conducted field experiments to test the hypothesis whether different type of miticide has a selecting pressure on mite size. This experiment did not give satisfactory results due to the variables that were not able to control in the field settings. Therefore, she decided to test this hypothesis in the lab, by exposing mites to amitraz coated glass vials.
She originally hypothesized that larger mites would be more tolerant to exposure to Amitraz, however she found the opposite after conducting resistance assays in lab settings. Additionally, she discovered that the feed state (i.e., access to host) of mites has a dramatic effect on Varroa’s tolerance of Amitraz exposure. Usually, when mite toxicity trials are performed, mites are harvested from adult bees, which are collected from colonies with high mite loads. As a side project Krisztina was experimenting with diets for mites and to her surprise, mites that were fed prior assay were dramatically more tolerant to exposure to Amitraz than mites that were not. As future work she seeks to verify this finding, testing this hypothesis with three types of miticide commonly used in beekeeping operations (Amitraz, Coumaphos, and Fluvalinate).
The knowledge gained from this work has important implications for the industry. A common and well-known need is the development of miticidal products to help beekeepers consistently control mite populations. If true, her findings that the diet and size of the mites affects their resistance to the miticide treatments suggest that the development of new products and their application regimes should consider mite size and mite feed state during toxicity screening. Further, this work could help explain the anecdotal claims by beekeepers that the same product does not have the same efficacy at different times of the year. Krisztina anticipates developing tools that predict treatment efficacy based on mite size and feeding state.