Description

VAR: Varroa Amitraz Resistance

Varroa destructor (VD) is a parasitic mite that infests honey bee colonies (Apis mellifera). These mites feed on the fat body tissue of adults and developing bees, weakening their hosts, facilitating the spread of pathogens, and resulting in colony decline and loss. Varroa mites continue to be the most significant threat to honey bee colonies on the national and global scale. To manage VD infestations, beekeepers have a few chemical options such as amitraz, an acaricide that targets and kills mites. However, like many pesticides, the prolonged use of amitraz has led to the development of resistant mite populations.

One of the target sites of amitraz within mites is the Octopamine β2 receptor (Oct), a G-protein coupled receptor. These receptors have multiple functions, including recognizing extracellular messengers, transducing signals to the cytosol, and mediating cellular responses needed for normal physiological functions in mites. At the start of this validation, two mutations within the Oct receptor have been associated with amitraz resistance: N87S and Y215H. The Y215H mutation is strongly associated with amitraz resistance and is the most prominent within American mite populations. The other mutation, N87S, is prominent in European mite populations. There appears to be a growing list of target-site mutations (e.g., F290L, Y337F) being discovered, indicating strong selective pressure of amitraz on mites.

In response to declining effectiveness of amitraz and the discovery of specific Oct receptor target-site mutations, the National Agricultural Genotyping Center (NAGC) explored two genotyping tests (N87S and Y215H) with the Y215H becoming the primary focus of this validation. The rapid genotyping test will enable beekeepers to assess resistance prevalence within their apiaries in real-time, providing valuable information to adjust their mite management to more effective treatment options.

References

Hernández-Rodríguez et al. (2022). Resistance to amitraz in the parasitic honey bee mite Varroa destructor is associated with mutations in the β-adrenergic-like octopamine receptor. Journal of Pest Science, 95(3), 1179-1195.

Lamas et al. (2025). Viruses and vectors tied to honey bee colony losses. bioRxiv, 2025-05.

Rinkevich et al. (2023). Confirmation of the Y215H mutation in the β2‐octopamine receptor in Varroa destructor is associated with contemporary cases of amitraz resistance in the United States. Pest Management Science, 79(8), 2840-2845.