In Silico Analysis of Potential Off-Target Effects of a Next-Generation dsRNA Acaricide for Varroa Mites (Varroa destructor) and Lack of Effect on a Bee-Associated Arthropod

Double-stranded RNA (dsRNA) biopesticides offer the potential for highly targeted pest control with minimal off-target impacts. Varroa mites (<i>Varroa destructor</i>) are an important pest of honey bees (<i>Apis mellifera</i>) 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 (<i>Danaus plexippus</i>), fruit flies (<i>Drosophila melanogaster</i>), and European earwigs (<i>Forficula auricularia</i>) showed theoretical potential for off-target effects. These <i>in silico</i> results could be used to help inform risk assessments. Second, we conducted vadescana feeding trials on the greater wax moth (<i>Galleria mellonella</i>), 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.