Search Results (5)

Double-stranded RNA (dsRNA) biopesticides offer the potential for highly targeted pest control with minimal off-target impacts. Varroa mites (Varroa destructor) are an important pest of honey bees (Apis mellifera) that are primarily managed by synthetic pesticides. A next-generation treatment using a varroa-active dsRNA, vadescana, has been developed to target calmodulin expression in varroa. We evaluated the potential exposure of non-target species to vadescana. First, we assessed potential gene silencing effects on 39 arthropods with known genomes via bioinformatics. Three mite species, monarch butterflies (Danaus plexippus), fruit flies (Drosophila melanogaster), and European earwigs (Forficula auricularia) showed theoretical potential for off-target effects. These in silico results could be used to help inform risk assessments. Second, we conducted vadescana feeding trials on the greater wax moth (Galleria mellonella), a common beehive associate. There were no significant differences in wax moth reproduction, survival, or adult F2 wing length between vadescana-fed and control groups. Male F2 body weight was slightly but significantly lower in wax moths exposed to the highest vadescana dose, with no such effect observed in female moths. Calmodulin gene expression was unaffected in wax moths. Our hazard assessment of vadescana’s lethal and sublethal effects on wax moths indicates minimal impact following continuous dietary exposure far greater than any exposure that might be expected in the field, in line with the bioinformatics findings. This biopesticide appears highly varroa-specific and likely has fewer non-target effects than many current varroa control methods. Full article

Background/Objectives: The increasing pressure from pathogens and parasites on Apis mellifera populations is resulting in significant colony losses. It is desirable to identify resistance-associated single-nucleotide polymorphisms (SNPs) and their variability for the purpose of breeding resilient honeybee lines. This study examined the genetic diversity of 13 SNPs previously studied for associations with various resistance-providing traits, including six linked to Varroa-specific hygiene, five linked to suppressed mite reproduction, one linked to immune response, and one linked to chalkbrood resistance. Methods: Genotyping was performed using a novel SNaPshot genotyping panel designed for this study. The sample pool consisted of 308 honeybee samples in total, covering all 77 administrative districts of the Czech Republic. Results: All examined loci were polymorphic. The frequency of positive alleles in our population is medium to low, depending on the specific SNP. An analysis of genotype frequencies revealed that most loci exhibited the Hardy–Weinberg equilibrium. A comparison of the allele and genotype frequencies of the same locus between samples from hives and samples from flowers revealed no significant differences. The genetic diversity, as indicated by the heterozygosity values, ranged from 0.05 to 0.50. The fixation index (F) was, on average, close to zero, indicating minimal influence of inbreeding or non-random mating on the genetic structure of the analyzed samples. Conclusions: The obtained results provide further insights into the genetic variation of SNPs associated with the immune response and resistance to pathogens in honeybee populations in the Czech Republic. This research provides a valuable foundation for future studies of honeybee diversity and breeding. Full article

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. Full article

Co-evolution is a major driving force shaping the outcome of host-parasite interactions over time. After host shifts, the lack of co-evolution can have a drastic impact on novel host populations. Nevertheless, it is known that Western honey bee (Apismellifera) populations can cope with host-shifted ectoparasitic mites (Varroa destructor) by means of natural selection. However, adaptive phenotypic traits of the parasites and temporal variations in host resistance behavior are poorly understood. Here, we show that mites made adaptive shifts in reproductive strategy when associated with resistant hosts and that host resistance traits can change over time. In a fully-crossed field experiment, worker brood cells of local adapted and non-adapted (control) A.mellifera host colonies were infested with mites originating from both types of host colonies. Then, mite reproduction as well as recapping of cells and removal of infested brood (i.e., Varroa Sensitive Hygiene, VSH) by host workers were investigated and compared to data from the same groups of host colonies three years earlier. The data suggest adaptive shifts in mite reproductive strategies, because mites from adapted hosts have higher probabilities of reproduction, but lower fecundity, when infesting their associated hosts than mites in treated colonies. The results confirm that adapted hosts can reduce mite reproductive success. However, neither recapping of cells nor VSH were significantly expressed, even though the latter was significantly expressed in this adapted population three years earlier. This suggests temporal variation in the expression of adaptive host traits. It also appears as if mechanisms not investigated here were responsible for the reduced mite reproduction in the adapted hosts. In conclusion, a holistic view including mite adaptations and studies of the same parasite/host populations over time appears overdue to finally understand the mechanisms enabling survival of V.destructor-infested honey bee host colonies. Full article

In the current context of worldwide honey bee colony losses, among which the varroa mite plays a major role, the hope to improve honey bee health lies in part in the breeding of varroa resistant colonies. To do so, methods used to evaluate varroa resistance need better understanding. Repeatability and correlations between traits such as mite non-reproduction (MNR), varroa sensitive hygiene (VSH), and hygienic behavior are poorly known, due to practical limitations and to their underlying complexity. We investigate (i) the variability, (ii) the repeatability of the MNR score, and (iii) its correlation with other resistance traits. To reduce the inherent variability of MNR scores, we propose to apply an empirical Bayes correction. In the short-term (ten days), MNR had a modest repeatability of 0.4, whereas in the long-term (a month), it had a low repeatability of 0.2, similar to other resistance traits. Within our dataset, there was no correlation between MNR and VSH. Although MNR is amongst the most popular varroa resistance estimates in field studies, its underlying complex mechanism is not fully understood. Its lack of correlation with better described resistance traits and low repeatability suggest that MNR needs to be interpreted cautiously, especially when used for selection. Full article