Occurrence and allele frequencies of genetic variants associated with Varroa drone brood resistance (DBR) in African Apis mellifera subspecies

Abstract

The ectoparasite Varroa destructor is a major contributor to the global decline of honeybee colonies (Apis mellifera), especially in the Northern Hemisphere. However, Varroa-resistant honeybee populations have been reported in various regions around the globe, including Europe and Africa. This resistance is primarily attributed to the trait known as Suppressed Mite Reproduction (SMR), which significantly reduces the reproductive success of Varroa mites within these colonies. Although this trait is still poorly understood, several efforts have been made to unravel the genetic basis of SMR. For example, a study in Belgium determined eight genetic variants in the honeybee genome that are associated with the infertility of mites in drone brood (Drone Brood Resistance or DBR). As these eight variants were found and validated in subpopulations of European subspecies only, there is limited knowledge about the occurrence of these markers in African honeybees. Hence, this study was designed to determine the allele frequencies of these eight genetic variants in African honeybee populations. More specifically, we used qPCR assays with dual-labeled probes to analyze bee samples collected from Benin, Ethiopia, and Uganda. Our results showed the presence of seven of the eight variants in African Apis mellifera subspecies, which may contribute to their innate resistance against the Varroa mite. Moreover, we found significant differences in allele frequencies among the three sampled African bee populations, suggesting the presence of genetic diversity within these populations, potentially altering their resistance to Varroa. This study revealed similar allele frequencies between African honeybees and bee samples from the European iberiensis-subspecies (A lineage), while Ethiopian bees showed distinct distributions, indicative of a unique lineage. Overall, the occurrence of most DBR-associated genetic variants in African honeybees opens research opportunities to elucidate the predictive properties and potential of these genetic variants in the African continent by examining genotype-phenotype associations.