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Simple Summary: Increasing honey bee resilience against the parasitic mite Varroa destructor, while respecting sustainability, may be achieved by enriching natural mite resistance traits in the breeding population. Some of these traits are linked to specific variants in the honey bee genome, which can be pinpointed and characterized with high-throughput molecular lab tests. Breeding by focusing on these genomic variants is thus more efficient and less time-consuming. However, when evaluating the link between a specific varroa resistance trait outcome and its associated variants in the genome, different contributions of the variants may be observed between honey bee races. It is hypothesized that these observations evolve from different linkages between the trait-causing genes and the genomic variants. Therefore, we evaluated the presence of genomic variants associated with a varroa resistance trait in different honey bee samples across the European continent. We observed significant differences in the presence of the genomic variants in the considered honey bee races, which underpin our hypothesis of linkage dissimilarities. This study shows that determining the honey bee race prior to using the genomic variants associated with varroa resistance for selective breeding is of utmost importance. Implementation of marker-assisted selection (MAS) in modern beekeeping would improve sustainability, especially in breeding programs aiming for resilience against the parasitic mite Varroa destructor. Selecting honey bee colonies for natural resistance traits, such as brood-intrinsic suppression of varroa mite reproduction, reduces the use of chemical acaricides while respecting local adaptation. In 2019, eight genomic variants associated with varroa non-reproduction in drone brood were discovered in a single colony from the Amsterdam Water Dune population in the Netherlands. Recently, a new study tested the applicability of these eight genetic variants for the same phenotype on a population-wide scale in Flanders, Belgium. As the properties of some variants varied between the two studies, one hypothesized that the difference in genetic ancestry of the sampled colonies may underly these contribution shifts. In order to frame this, we determined the allele frequencies of the eight genetic variants in more than 360 Apis mellifera colonies across the European continent and found that variant type allele frequencies of these variants are primarily related to the A. mellifera subspecies or phylogenetic honey bee lineage. Our results confirm that population-specific genetic markers should always be evaluated in a new population prior to using them in MAS programs. [ABSTRACT FROM AUTHOR]

Over the last few years, the honeybees faced a significant decline worldwide. Despite many biotic and abiotic stressors, one of the leading causes of honeybee colony loses is Varroa destructor, followed by Nosema spp.. Given the importance of honeybee in agriculture and a significantly increased resistance to treatments identified in Varroa destructor, a more sustainable method to counter this mite is needed. One of these sustainable methods is breeding for resistance to Varroa destructor. Due to the rising number of honeybee populations with potential resistance to Varroa destructor, a new promising breeding plan for natural selection was proposed. This breeding plan was adapted and implemented on a local population of honey bees in Transilvania, with the primary objective of obtaining resistant colonies to Varroa destructor. Development of these colonies was observed, and analysis of Varroa infestation level and Nosema spp. was performed to assess the health status of the population or the cause of mortality. [ABSTRACT FROM AUTHOR]

Varroa destructor is a parasitic mite that represents a major global threat for the Western honeybee Apis mellifera. This parasite managed to switch from its natural host the Eastern honeybee, A. cerana, and within a few decades, it spread among A. mellifera populations around the world. Today beekeepers are using a variety of different acaricides to keep the parasite population under control. However, for many of these substances, the parasite evolved resistance asking for the development of novel compounds. Hence the treatment is less suited as a sustainable tool in honeybee health; consequently, other alternative options are needed, and breeding of Varroa resistant honeybees have been suggested as a more sustainable solution. Here we reviewed the successful efforts and the apicultural procedures needed to be implemented to achieve resistant honeybees. We also describe the underlying resistance mechanisms and discuss the benefits of breeding within regional populations, considering the biodiversity aspects of A. mellifera. [ABSTRACT FROM AUTHOR]

Social insect colonies possess a range of defences which protect them against highly virulent parasites and colony collapse. The host–parasite interaction between honey bees (Apis mellifera) and the mite Varroa destructor is unusual, as honey bee colonies are relatively poorly defended against this parasite. The interaction has existed since the mid‐20th Century, when Varroa switched host to parasitize A. mellifera. The combination of a virulent parasite and relatively naïve host means that, without acaricides, honey bee colonies typically die within 3 years of Varroa infestation. A consequence of acaricide use has been a reduced selective pressure for the evolution of Varroa resistance in honey bee colonies. However, in the past 20 years, several natural‐selection‐based breeding programmes have resulted in the evolution of Varroa‐resistant populations. In these populations, the inhibition of Varroa's reproduction is a common trait. Using a high‐density genome‐wide association analysis in a Varroa‐resistant honey bee population, we identify an ecdysone‐induced gene significantly linked to resistance. Ecdysone both initiates metamorphosis in insects and reproduction in Varroa. Previously, using a less dense genetic map and a quantitative trait loci analysis, we have identified Ecdysone‐related genes at resistance loci in an independently evolved resistant population. Varroa cannot biosynthesize ecdysone but can acquire it from its diet. Using qPCR, we are able to link the expression of ecdysone‐linked resistance genes to Varroa's meals and reproduction. If Varroa co‐opts pupal compounds to initiate and time its own reproduction, mutations in the host's ecdysone pathway may represent a key selection tool for honey bee resistance and breeding. see also the Perspective by Evans [ABSTRACT FROM AUTHOR]