A metatranscriptomic analysis of diseased social wasps (Vespula vulgaris) for pathogens, with an experimental infection of larvae and nests.

Oliver Quinn,Mariana Bulgarella,James W Baty,Philip J Lester,Robert L Brown,Monica A M Gruber,Olav Rueppell

doi:10.1371/journal.pone.0209589

Oliver Quinn, Mariana Bulgarella + Show 5 more

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https://doi.org/10.1371/journal.pone.0209589

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Abstract

Social wasps are a major pest in many countries around the world. Pathogens may influence wasp populations and could provide an option for population management via biological control. We investigated the pathology of nests of apparently healthy common wasps, Vespula vulgaris, with nests apparently suffering disease. First, next-generation sequencing and metatranscriptomic analysis were used to examine pathogen presence. The transcriptome of healthy and diseased V. vulgaris showed 27 known microbial phylotypes. Four of these were observed in diseased larvae alone (Aspergillus fumigatus, Moellerella wisconsensis, Moku virus, and the microsporidian Vavraia culicis). Kashmir Bee Virus (KBV) was found to be present in both healthy and diseased larvae. Moellerella wisconsensis is a human pathogen that was potentially misidentified in our wasps by the MEGAN analysis: it is more likely to be the related bacteria Hafnia alvei that is known to infect social insects. The closest identification to the putative pathogen identified as Vavraia culicis was likely to be another microsporidian Nosema vulgaris. PCR and subsequent Sanger sequencing using published or our own designed primers, confirmed the identity of Moellerella sp. (which may be Hafnia alvei), Aspergillus sp., KBV, Moku virus and Nosema. Secondly, we used an infection study by homogenising diseased wasp larvae and feeding them to entire nests of larvae in the laboratory. Three nests transinfected with diseased larvae all died within 19 days. No pathogen that we monitored, however, had a significantly higher prevalence in diseased than in healthy larvae. RT-qPCR analysis indicated that pathogen infections were significantly correlated, such as between KBV and Aspergillus sp. Social wasps clearly suffer from an array of pathogens, which may lead to the collapse of nests and larval death.

Highlights

Social wasps can be a major pest in their introduced range
We performed metatranscriptomic comparative analyses using RNA-seq to elucidate the cause of V. vulgaris larvae symptomatic of an unknown infection
The first four of these candidates were identified in the diseased larvae alone, with Kashmir Bee Virus (KBV) identified in both diseased and healthy wasps

Summary

Introduction

Social wasps can be a major pest in their introduced range. In countries such as New Zealand, Vespula germanica and V. vulgaris are considered to be amongst the most damaging and widespread invertebrate pests [1]. First observed in 1921, V. vulgaris has become especially abundant, most notably in New Zealand beech forests (Fuscospora spp.), with densities exceeding 370 wasps m-2 of tree trunk and up to 40 nests ha-1 [2,3]. They are major predators of native invertebrates, competitively excluding native birds and estimated to cost New Zealand’s economy more than NZ$133 million per annum. Many pathogens and parasites have been identified, to date no effective biocontrol has been successful and vespid wasps continue to proliferate in newly acquired ranges such as New Zealand and Argentina [4]. It was noted at the time that this apparent but undetermined pathogen appeared virulent, causing infections to spread to other close-by experimental wasp nests housed in a glasshouse [10]

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