Abstract
The parasitic mite Varroa destructor has a significant worldwide impact on bee colony health. In the absence of control measures, parasitized colonies invariably collapse within 3 years. The synthetic pyrethroids tau-fluvalinate and flumethrin have proven very effective at managing this mite within apiaries, but intensive control programs based mainly on one active ingredient have led to many reports of pyrethroid resistance. In Europe, a modification of leucine to valine at position 925 (L925V) of the V. destructor voltage-gated sodium channel was correlated with resistance, the mutation being found at high frequency exclusively in hives with a recent history of pyrethroid treatment. Here, we identify two novel mutations, L925M and L925I, in tau-fluvalinate resistant V. destructor collected at seven sites across Florida and Georgia in the Southeastern region of the USA. Using a multiplexed TaqMan® allelic discrimination assay, these mutations were found to be present in 98% of the mites surviving tau-fluvalinate treatment. The mutations were also found in 45% of the non-treated mites, suggesting a high potential for resistance evolution if selection pressure is applied. The results from a more extensive monitoring programme, using the Taqman® assay described here, would clearly help beekeepers with their decision making as to when to include or exclude pyrethroid control products and thereby facilitate more effective mite management programmes.
Highlights
The ectoparasitic mite Varroa destructor Anderson and Trueman (Arachnida: Acari: Varroidae) causes severe damage to colonies of the Western honey bee (Apis mellifera L.) in many countries worldwide
We report the identification of two alternative amino acid substitutions, L925M and L925I, in the voltagegated sodium channel (VGSC) of populations of V. destructor originating from seven different locations across the Southeastern USA
TaqMan1 allelic discrimination assays designed to detect the L925V mutation that was previously described in pyrethroid-resistant V. destructor samples collected in Central/Southern
Summary
The ectoparasitic mite Varroa destructor Anderson and Trueman (Arachnida: Acari: Varroidae) causes severe damage to colonies of the Western honey bee (Apis mellifera L.) in many countries worldwide. It is considered to be one of the most important problems for modern apiculture and a key factor leading to the high annual losses of honey bee colonies in recent years [1], posing a serious risk for pollination. Varroa destructor causes direct damage to bees by feeding on the haemolymph of immature and adult bees, and it serves as a vector for several bee viruses that contribute to a progressive decline of bee colonies [4,5,6]. In the absence of an effective control program, parasitized colonies will usually collapse in less than 3 years. Many beekeepers tend to rely exclusively on a few active ingredients, with the synthetic pyrethroids tau-fluvalinate and flumethrin being amongst the most popular varroacides due to their relative low toxicity towards bees, ease of application and high efficacy, eliminating up to
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