An <scp>RNA</scp> interference biopesticide reduces reproduction of the honey bee parasite <i>Varroa destructor</i> by down‐regulating embryo development pathways
Zoe E. Smeele, Rose A. McGruddy, James W. Baty, Brian Manley, Kenneth E. Narva, Emma De Neef, Eric R. L. Gordon, Upendra Kumar Devisetty, Katie Youngs, Antoine Felden, Philip J. Lester
Abstract
BACKGROUND: The honey bee parasite, Varroa destructor, is a globally devastating pest. Our previous experiments with laboratory mini-hives of bees and Varroa have shown an RNA interference biopesticide consisting of double-stranded RNA specific in sequence to a V. destructor calmodulin gene (named Norroa™, with the active ingredient vadescana) can substantially reduce Varroa reproduction. Here, we used a similar experimental design to examine the transcriptomic effects of vadescana on these parasites. RESULTS: Consistent with previous results, Varroa reproduction was significantly reduced in vadescana treated mini-hives with no effect on foundress survival. Calmodulin expression was only significantly reduced in vadescana-treated mites sampled 5 days after brood cell capping. While RNAseq and qPCR results showed the apparent recovery of gene expression by the foundress mites by the time that bees emerged from the pupal cells, this recovery was insufficient to enable successful Varroa reproduction. Gene ontology results showed that calcium ion binding and cadherin related genes engaged in processes associated with cell adhesion and embryo development were significantly down-regulated in vadescana 2 and 8 g/L treated mites. CONCLUSION: Our study shows the effects of vadescana on Varroa reproduction occur early in the reproductive cycle, as no offspring were produced by foundress mites sampled 5 days after cell capping and calmodulin expression was significantly reduced in mites sampled from brood cells at this time. These findings inform our understanding of Varroa reproduction by showing that calmodulin-mediated calcium signaling plays a critical role in early embryogenesis and reproduction in these parasites. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.