Amitraz Resistance in French Varroa Mite Populations-More Complex Than a Single-Nucleotide Polymorphism

Area of Science:

• Veterinary Entomology
• Molecular Entomology
• Pest Management

Background:

• Amitraz is a key acaricide for controlling Varroa mite infestations in honey bee colonies.
• Increasing reports indicate reduced efficacy of amitraz treatments, raising concerns among beekeepers.
• Varroa mite resistance threatens effective Varroa management and honey bee colony health.

Purpose of the Study:

• To investigate the field efficacy of an amitraz-based treatment (Apivar®) in French apiaries.
• To assess the sensitivity of Varroa mites to amitraz through laboratory assays.
• To genotype Varroa mites for genetic markers associated with amitraz resistance, specifically focusing on the octopamine receptor gene.

Main Methods:

• Field efficacy trials of Apivar® in French apiaries (2020-2021).
• Laboratory bioassays to determine amitraz sensitivity (LC90) of Varroa mites.
• Genotyping of 240 Varroa mites from various French regions to analyze the ORβ-2R-L gene, focusing on a specific single-nucleotide polymorphism (SNP).

Main Results:

• Amitraz resistance in Varroa mites was confirmed in French apiaries, exhibiting a patchy distribution or "islands of resistance."
• The reduction in treatment efficacy due to amitraz resistance was less severe than observed with pyrethroid or coumaphos resistance.
• Genetic analysis cast doubt on the hypothesis that a specific SNP at position 260 of the ORβ-2R-L gene is the sole driver of amitraz resistance.

Conclusions:

• Amitraz resistance is a confirmed phenomenon in French Varroa mite populations.
• The genetic basis of amitraz resistance may be more complex than previously assumed, with the studied SNP not being solely responsible.
• Continued monitoring and research are crucial for developing sustainable Varroa mite management strategies.