Deformed wing virus type A, a major honey bee pathogen, is vectored by the mite Varroa destructor in a non-propagative manner

Authors: POSADA, FRANCISCO - Oak Ridge Institute For Science And Education (ORISE); Childers, Anna; Heerman, Matthew; EGEKWU, NOBLE - University Of Florida; Cook, Steven; Chen, Yanping - Judy; Evans, Jay; RYABOV, EUGENE - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2019
Publication Date: 8/27/2019
Citation: Posada, F., Childers, A.K., Heerman, M.C., Egekwu, N., Cook, S.C., Chen, Y., Evans, J.D., Ryabov, E.V. 2019. Deformed wing virus type A, a major honey bee pathogen, is vectored by the mite Varroa destructor in a non-propagative manner. Scientific Reports. 9(1):1244. https://doi.org/10.1038/s41598-019-47447-3.
DOI: https://doi.org/10.1038/s41598-019-47447-3

Interpretive Summary: Varroa destructor mites transfer viruses between honey bees, adding to their devastating impact. One virus that greatly benefits from Varroa transmission is Deformed wing virus (DWV). It has long been predicted that this virus replicates (produces new copies of itself) inside Varroa mites. Using careful trials, where viruses and mites were introduced to developing honey bees, we show that, at least for DWV strain 'A', viruses do not actively grow in their Varroa vectors. This has strong implications for virulence in these viruses, and more generally for the maintenance of damaging viruses in honey bee colonies and the environment. Specially, these surprising results indicated that any steps to isolate mites from bees until non-reproducing viruses are inactivated might offer an effective control against mite-transported DWV. Also, the focus of research and potential controls should focus on mechanisms used by DWV to invade and exploit honey bee cells, not those of the mites that help move them.

Technical Abstract: Honey bees, the primary managed insect pollinator, suffer considerable losses due to Deformed wing virus (DWV), an RNA virus vectored by the mite Varroa destructor. Mite vectoring has resulted in the emergence of virulent DWV variants. The basis for such changes in DWV is poorly understood. Most importantly, it remains unclear whether replication of DWV occurs in the mite. In this study, we exposed Varroa mites to DWV type A via feeding on artificially infected honey bees. A significant, 357-fold increase in DWV load was observed in these mites after 2 days. However, after 8 additional days of passage on honey bee pupae with low viral loads, the DWV load dropped by 29-fold. This decrease significantly reduced the mites’ ability to transmit DWV to honey bees. Notably, negative-strand DWV RNA, which could indicate viral replication, was detected only in mites collected from pupae with high DWV levels but not in the passaged mites. We also found that Varroa mites contain honey bee mRNAs, consistent with the acquisition of honey bee cells which would additionally contain DWV replication complexes with negative-strand DWV RNA. We propose that transmission of DWV type A by Varroa mites occurs in a non-propagative manner.