Honey bee genetic stock determines DWV symptom severity but not viral load or dissemination following pupal exposure

Authors: Penn, Hannah; Simone-Finstrom, Michael; Chen, Yanping - Judy; HEALY, KRISTEN - Louisiana State University Agcenter

Submitted to: Frontiers in Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2022
Publication Date: 6/3/2022
Citation: Penn, H.J., Simone-Finstrom, M.D., Chen, Y., Healy, K.B. 2022. Honey bee genetic stock determines DWV symptom severity but not viral load or dissemination following pupal exposure. Frontiers in Genetics. 13:909392. https://doi.org/10.3389/fgene.2022.909392.
DOI: https://doi.org/10.3389/fgene.2022.909392

Interpretive Summary: Honeybee parasites and viruses spread by the mite can harm the bee colony by causing crumpled wings on bees. The Varroa mite often attaches to juvenile honeybees resulting in a loss in colony productivity and death. Examples of productivity losses are seen in bee rearing, food collection, and colony defense. Therefore, we conducted experiments to understand if bees with different genetic backgrounds, some more effective at mite-removal, also exhibit differences in infection levels and symptoms as adults. While bee genetics did not impact virus levels in individual bees, some bees were more tolerant of the virus and displayed less symptoms like crumpled wings after exposure. Our study indicates that while certain bees are more effective at preventing mite infestation in the colony, those same bees can be susceptible to debilitating physical symptoms (wing deformities) from a mite-vectored virus.

Technical Abstract: Bees exposed to Varroa mites incur substantial physical damage in addition to potential exposure to vectored viruses such as Deformed wing virus (DWV) that exists as three master variants (DWV-A, DWV-B, and DWV-C) and recombinants. Although mite-resistant bees have been primarily bred to mitigate the impacts of Varroa mites, mite resistance may be associated with increased tolerance or resistance to the vectored viruses. The goal of our study was to determine if five honey bee stocks (Carniolan, Italian, Pol-Line, Russian, and Saskatraz) differ in their resistance or tolerance to DWV based on prior breeding for mite resistance. We injected white-eyed pupae with a sublethal dose (105) of DWV or exposed them to mites then evaluated DWV levels and dissemination as well as morphological symptoms upon adult emergence. While we found no evidence of DWV resistance across stocks (i.e., similar rates of viral replication and dissemination), we observed that some stocks exhibited reduced symptom severity suggestive of differential tolerance. However, DWV tolerance was not consistent across mite-resistant stocks as Russian bees were most tolerant while Pol-Line exhibited the most severe symptoms. DWV variants A and B exhibited differential dissemination patterns that interacted significantly with treatment group but not bee stock. Further, elevated DWV-B levels reduced adult emergence time while both DWV variants were associated with symptom likelihood and severity. These data indicate that the genetic differences underlying bee resistance to Varroa mites are not necessarily correlated with DWV tolerance and may interact differentially with DWV variants, highlighting the need for further work on mechanisms of tolerance and bee stock-specific physiological interactions with pathogen variants.