Abstract
Around 14 distinct virus species-complexes have been detected in honeybees, each with one or more strains or sub-species. Here we present the initial characterization of an entirely new virus species-complex discovered in honeybee (Apis mellifera L.) and varroa mite (Varroa destructor) samples from Europe and the USA. The virus has a naturally poly-adenylated RNA genome of about 6500 nucleotides with a genome organization and sequence similar to the Tymoviridae (Tymovirales; Tymoviridae), a predominantly plant-infecting virus family. Literature and laboratory analyses indicated that the virus had not previously been described. The virus is very common in French apiaries, mirroring the results from an extensive Belgian survey, but could not be detected in equally-extensive Swedish and Norwegian bee disease surveys. The virus appears to be closely linked to varroa, with the highest prevalence found in varroa samples and a clear seasonal distribution peaking in autumn, coinciding with the natural varroa population development. Sub-genomic RNA analyses show that bees are definite hosts, while varroa is a possible host and likely vector. The tentative name of Bee Macula-like virus (BeeMLV) is therefore proposed. A second, distantly related Tymoviridae-like virus was also discovered in varroa transcriptomes, tentatively named Varroa Tymo-like virus (VTLV).
Highlights
Honeybees (Apis mellifera L.) are hosts to a large number of viruses [1,2]
The origin of the present discovery was two clones, obtained inadvertently during the cloning and sequencing of deformed wing virus (DWV) in Pennsylvania in 2001 [6]. The sequences of these clones were distantly-related to the RNA-dependent RNA polymerase (RdRp) and capsid protein (CP) of Tymoviruses, a group of viruses infecting plants and transmitted by phloem-sucking insects [24,25], and were, initially thought to belong to a contaminating plant virus
Since Varroa destructor is an obligate parasite that only feeds on bee haemolymph [28], and has no contact at all with plants, the possibility arose that these “contaminant” sequences could, represent a true virus of honeybees or their parasites
Summary
Honeybees (Apis mellifera L.) are hosts to a large number of viruses [1,2]. Most were discovered and characterized serologically during the 1970s and 1980s at Rothamsted Research International and many have recently been sequenced [2]. As many as 26 virus-like entities have been described, many of these are closely related by serology [1,3] or nucleotide identity [4,5] and a more accurate description is one of 14 distinct honeybee virus species-complexes, each with a spectrum of closely related, but unique viruses [2,4,5]. We describe the discovery, genomic characterization, and distribution of a new virus species-complex, found naturally in honeybees and its parasitic ectoparasite, Varroa destructor, related to Macula-, Marafi- and Tymoviruses (Tymovirales; Tymoviridae)
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