HIGH PREVALENCE OF THE F290L AMITRAZ-RESISTANCE ALLELE IN VARROA DESTRUCTOR POPULATIONS FROM PORTUGAL
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resumo
The Western honey bee (Apis mellifera) has a crucial role in pollination and apicultural production but faces a major threat from the ectoparasitic mite Varroa destructor. This parasite causes varroosis and acts as a vector for multiple viruses, undermining colony health and survival. Chemical control relies mainly on two classes of synthetic acaricides: pyrethroids (fluvalinate and flumethrin) and formamidines (amitraz). However, the repeated and prolonged use of these compounds has promoted the development of resistance in V. destructor populations. Amitraz resistance has been associated with mutations in the Octopamine-like β-adrenergic receptor (Octβ2R), including N87S (France), Y215H (USA), F290L (Spain), and Y337F (Turkey). Until now, the distribution of these resistance alleles had not been investigated in Portugal. To address this gap, mites collected from different regions of the country were analysed through DNA extraction, PCR with specific primers, and Sanger sequencing. The results revealed an unexpectedly high frequency (98.3%) of the F290L allele, which has also been reported in Spanish populations, suggesting a strong potential selective pressure resulting from the prolonged use of amitraz. This atypically high frequency raises important questions regarding the origin and evolutionary trajectory of this resistance allele in Portugal. Therefore, a retrospective analysis of mite samples collected before the widespread adoption of amitraz is proposed. This approach will clarify whether the F290L allele was already present in ancestral V. destructor populations or whether its current prevalence arose from recent selective pressure. Integrating this data will be essential for understanding the evolutionary dynamics of resistance and for supporting the development of more effective monitoring and management strategies against this parasite.
