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

Francisco Posada-Florez,Noble I Egekwu,Steven C Cook,Matthew C Heerman,Jay D Evans,Yanping Chen,Anna K Childers,Eugene V Ryabov

doi:10.1038/s41598-019-47447-3

Francisco Posada-Florez, Noble I Egekwu + Show 6 more

Open Access

https://doi.org/10.1038/s41598-019-47447-3

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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.

Highlights

Honey bee (Apis mellifera), the primary managed insect pollinator, suffers considerable losses caused by pathogens[1,2], including Deformed wing virus (DWV)[3], which endanger pollination service worldwide[4,5]
Strong positive correlation of DWV loads was reported in naturally infested colonies between the Varroa mites and associated honey bee pupae, this cannot be used as an argument in support of DWV replicates within Varroa mainly because DWV is vectored by mites and could be acquired by the mites from the same pupae which they infect
Significant increases and decreases in DWV loads in Varroa mites following feeding on pupae with different DWV levels

Summary

Introduction

Honey bee (Apis mellifera), the primary managed insect pollinator, suffers considerable losses caused by pathogens[1,2], including Deformed wing virus (DWV)[3], which endanger pollination service worldwide[4,5]. Strong positive correlation of DWV loads was reported in naturally infested colonies between the Varroa mites and associated honey bee pupae, this cannot be used as an argument in support of DWV replicates within Varroa mainly because DWV is vectored by mites and could be acquired by the mites from the same pupae which they infect. We investigated temporal dynamics of both positive and negative-strand DWV-A RNA accumulation in Varroa mites and honey bee pupae, as well as transmission of the virus between mites and pupae. We found no evidence supporting DWV-A replication in the Varroa mites, demonstrating that virus loads in the mite are highly dynamic, and that the mites’ ability to transmit DWV significantly declines following loss of their DWV loads after feeding on the honey bees with low DWV levels

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