A new mutation in the octopamine receptor associated with amitraz resistance in Varroa destructor.

BACKGROUND: The acaricide amitraz is now used intensively in many regions to control the honey bee parasite, Varroa destructor, because of the reduced efficacy of pyrethroids and coumaphos caused by resistance evolution. The continued application of amitraz in recent years exerts a very high selection pressure on mites, favouring the evolution of resistance to this acaricide. Mutations N87S and Y215H in the ß2-adrenergic-like octopamine receptor (Octß2R), target site of amitraz, have been already associated with resistance to amitraz in France and the USA, respectively. RESULTS: A new mutation (F290L) in the Octß2R of V. destructor has been found in mites from Spanish apiaries. The frequency of L290 mutated alleles in colonies increased after consecutive treatments with amitraz. In a field trial, mites from colonies with higher frequency of L290 mutated allele took longer to die compared with those carrying a higher proportion of the wild-type allele. Lower susceptibility to amitraz was found in apiaries with a high frequency of homozygous mutants. CONCLUSION: Our data indicate the association of the F290L mutation in the octopamine receptor with resistance to amitraz in Spanish populations of V. destructor. Determining the frequency of mutant mites in apiaries may be important for predicting the efficacy of amitraz treatment in the field and would help design appropriate resistance management. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Confirmation of the Y215H mutation in the ß2 -octopamine receptor in Varroa destructor is associated with contemporary cases of amitraz resistance in the United States.

BACKGROUND: The parasitic mite, Varroa destructor (Anderson and Trueman), is a leading cause of honey bee colony losses around the world. Application of miticides such as amitraz are often the primary method of Varroa control in commercial beekeeping operations in the United States. It is likely that excessive and exclusive amitraz application has led to the development of amitraz resistance in Varroa. A mutation of tyrosine at amino acid position 215 to histidine (Y215H) in the ß2 -octopamine receptor was identified in putatively amitraz-resistant Varroa in the United States. This research investigated the presence of the Y215H mutation in quantitatively confirmed amitraz-resistant Varroa from the United States. RESULTS: There was a strong association of susceptible and resistant phenotypes with the corresponding susceptible and resistant genotypes respectively, and vice versa. The resistance bioassay may understate resistance levels because of the influence of environmental conditions on the outcome of the test, whereby Varroa with an amitraz-resistant genotype may appear with a susceptible phenotype. CONCLUSION: Confirmation of the Y215H mutation in the ß2 -octopamine receptor of amitraz-resistant Varroa encourages the development and validation of low-cost, high-throughput genotyping protocols to assess amitraz resistance. Resistance monitoring via genotyping will allow for large-scale passive monitoring to accurately determine the prevalence of amitraz resistance rather than directed sampling of apiaries with known resistance issues. Genotyping of Varroa for amitraz resistance early in the beekeeping season may predict late-season resistance at the colony level and provide beekeepers with enough time to develop an effective Varroa management strategy. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.