Comparison of tau-fluvalinate, acrinathrin, and amitraz effects on susceptible and resistant populations of Varroa destructor in a vial test

Abstract

The parasitic mite Varroa destructor is a major pest of the western honeybee, Apis mellifera. The development of acaricide resistance in Varroa populations is a global issue. Discriminating concentrations of acaricides are widely used to detect pest resistance. Two methods, using either glass vials or paraffin capsules, are used to screen for Varroa resistance to various acaricides. We found the glass vial method to be useless for testing Varroa resistance to acaridices, so we developed a polypropylene vial bioassay. This method was tested on tau-fluvalinate-, acrinathrin-, and amitraz-resistant mite populations from three apiaries in Czechia. Acetone was used as a control and technical grade acaricide compounds diluted in acetone were applied to the polypropylene vials. The solutions were spread on the vial surface by rolling the vial, and were then evaporated. Freshly collected Varroa females were placed in the vials and the mortality of the exposed mites was measured after 24 h. The Varroa populations differed in mortality between the apiaries and the tested compounds. Mites from the Kyvalka site were resistant to acrinathrin, tau-fluvalinate, and amitraz, while mites from the Postrizin site were susceptible to all three acaricides. In Prelovice apiary, the mites were susceptible to acrinathrin and amitraz, but not to tau-fluvalinate. The calculated discriminating concentrations for tau-fluvalinate, acrinathrin, and amitraz were 0.66, 0.26 and 0.19 µg/mL, respectively. These results indicate that polyproplyne vial tests can be used to determine discriminating concentrations for the early detection of acaricide resistant Varroa. Finally, multiple-resistance in Kyvalka may indicate metabolic resistance.

Detection of amitraz resistance and reduced treatment efficacy in the Varroa Mite, Varroa destructor, within commercial beekeeping operations

“…This difference in threshold for resistance determination may be the consequence of differences in the slope of the concentration-response curves for amitraz and fluvalinate. In this study, the high slope of the amitraz concentration-response curve was 3.94 in the susceptible USDA Lab Varroa population, while the slope of fluvalinate concentration-response curves for fluvalinate-susceptible Varroa is near 1 [39,41]. This is critical because in concentrationresponse curves with high slopes, small changes in concentration may cause large changes in survivorship, while large changes in concentration are necessary to induce small changes in survivorship in concentration-response curves with low slopes.…”

“…The fact that nearly half of the commercial beekeeping operations that have relied on amitraz for Varroa control for at least 3 years did not yield enough Varroa to test for amitraz resistance is evidence of the ongoing effectiveness of this treatment. The isolated reports of Varroa control failure due to amitraz resistance [37][38][39] despite a long history of intense and frequent amitraz use is peculiar as there are numerous widespread reports of Varroa control failure due to high levels of resistance to fluvalinate [17,32,46,47] and coumaphos [33,[48][49][50]. The low amitraz LC 50 in the USDA lab population validates it use as an amitraz-susceptible reference population.…”

“…Despite a plethora of circumstantial suggestions, the mostly likely explanation of reduced Varroa control via amitraz indicates amitraz-resistant Varroa populations. Amitraz resistance in Varroa is plausible because isolated incidents of amitraz resistance were reported in the USA [37], Argentina [38], and Czechia [39]. However, widespread amitraz resistance in Varroa in commercial beekeeping operations has not been documented in the USA.…”

tau‐Fluvalinate and other pesticide residues in honey bees before overwintering

“…tau ‐Fluvalinate is one of the most important active compounds used to control Varroa ; however, extensive and repeated use of tau ‐fluvalinate contributes to the selection of resistant mite populations and hampers the efficacy of the varroacide . A point mutation in the sodium channel gene has been described as a mechanism of Varroa resistance towards tau ‐fluvalinate .…”

“…12 tau-Fluvalinate is one of the most important active compounds used to control Varroa; however, extensive and repeated use of tau-fluvalinate contributes to the selection of resistant mite populations and hampers the efficacy of the varroacide. [20][21][22][23][24][25] A point mutation in the sodium channel gene has been described as a mechanism of Varroa resistance towards tau-fluvalinate. [26][27][28][29][30][31] For long-term control, tau-fluvalinate is applied to the hive in the form of plastic strips through commercial products such as Apistan.…”