Summary 1.Many studies have searched for traits that characterize successful invaders. Unfortunately, very few generalizations have emerged from this work. It seems that the traits of successful invaders are idiosyncratic and context-dependent. Unless we are to study each potential invader in each possible target community individually, we will need a new approach. 2. We introduce a framework for predicting traits that are likely to confer success in a given ecosystem. Our approach considers the prevailing environmental conditions, the traits of resident species, and the traits of potentially invading species. 3. Our approach can be applied to ecosystems where the environmental conditions and/or disturbance regime have recently changed, to predict the range of trait space occupied by (i) native species at risk of local extinction, (ii) native species that can persist under the present conditions, and (iii) successful invaders. Our approach can also be used to identify unoccupied viable trait space (i.e. vacant niches) that might be at risk of invasion. 4. Synthesis . Understanding invasions resulting from rapid changes in environmental conditions and invasions resulting from the colonization of vacant niches would be a major step forward for invasion biology. The conceptual framework described here is not limited to plant invasions: the same approach can be used for any taxa (e.g. insects, fish, mammals and marine invertebrates) and could also be used to predict species responses to environmental change.

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Social insects host a diversity of viruses. We examined New Zealand populations of the globally widely distributed invasive Argentine ant (Linepithema humile) for RNA viruses. We used metatranscriptomic analysis, which identified six potential novel viruses in the Dicistroviridae family. Of these, three contigs were confirmed by Sanger sequencing as Linepithema humile virus-1 (LHUV-1), a novel strain of Kashmir bee virus (KBV) and Black queen cell virus (BQCV), while the others were chimeric or misassembled sequences. We extended the known sequence of LHUV-1 to confirm its placement in the Dicistroviridae and categorised its relationship to closest relatives, which were all viruses infecting Hymenoptera. We examined further for known viruses by mapping our metatranscriptomic sequences to all viral genomes, and confirmed KBV, BQCV, LHUV-1 and Deformed wing virus (DWV) presence using qRT-PCR. Viral replication was confirmed for DWV, KBV and LHUV-1. Viral titers in ants were higher in the presence of honey bee hives. Argentine ants appear to host a range of' honey bee' pathogens in addition to a virus currently described only from this invasive ant. The role of these viruses in the population dynamics of the ant remain to be determined, but offer potential targets for biocontrol approaches.Social insects carry a range of viruses that can have a major effect on host population dynamics. Perhaps the best known viral community is from honey bees, which has been the focus of considerable study due to their economic importance. A range of different factors are likely to contribute to colony collapse and bee declines in general, with viruses frequently considered key players 1, 2 . A recent review noted honey bees host 24 viruses, primarily in the Dicistroviridae and Iflaviridae families 3 . Of these, the Deformed wing virus (DWV) has been suggested as a likely candidate for the majority of global honey bee colony losses during the past 50 years 4 . Such viruses, however, are not restricted to honey bees. There is increasing evidence that these 'honey bee' viruses are common in a wide range of insect hosts [5][6][7] . Other social insects have been found to carry their own unique suites of viral pathogens. For example, over the last decade four viruses have been described from the red imported fire ant (Solenopsis invicta) 8 . These were the first viruses fully described from ants. Three of these viruses are positive-sense, single-stranded RNA (ssRNA) viruses, with one (Solenopsis invicta virus-1, SINV-1) assigned taxonomically to the Dicistroviridae family, one (Solenopsis invicta virus-3, SINV-3) in a proposed new family, Solinviviridae 9 and the third currently unclassified (Solenopsis invicta virus-2, SINV-2) 8, 9 ; The fourth virus is a DNA virus, and has been placed in the family Parvoviridae 10 . One of the three ssRNA viruses, SINV-3, shows promise as a biocontrol agent as it can cause significant mortality in laboratory fire ant colonies 11 . Metatranscriptomic and pyrosequencing techniques have proven particula...

Aim Understanding the role of enemy release in biological invasions requires an assessment of the invader's home range, the number of invasion events and enemy prevalence. The common wasp (Vespula vulgaris) is a widespread invader. We sought to determine the Eurasian origin of this wasp and examined world‐wide populations for microsporidian pathogen infections to investigate enemy release. Location Argentina, Eurasia, New Zealand. Methods A haplotype network and phylogenetic tree were constructed from combined wasp COI and cytb mitochondrial markers. A morphometric study using canonical discriminant analysis was conducted on wing venation patterns. Microsporidian pathogens prevalence was also examined using small subunit rRNA microsporidia‐specific primers. Results Our spatially structured haplotype network from the native range suggested a longitudinal cline of wasp haplotypes along an east to west gradient. Six haplotypes were detected from New Zealand, and two from Argentina. The populations from the introduced range were genetically similar to the western European, United Kingdom and Ireland. The morphometric analysis showed significant morphological variation between countries and supported the Western European origin for New Zealand populations, although not for Argentine samples. Microsporidian infection rates were highest in New Zealand samples (54%), but no significant differences in infection rates were observed between the invaded and native range. Nosema species included matches to N. apis (a pathogen from honey bees) and N. bombi (from bumble bees). Main conclusions Multiple introductions of the common wasp have occurred in the invaded range. A high microsporidian infection rate within the native range, combined with multiple introductions and a reservoir of pathogens in other social insects such as bees, likely contributes to the high microsporidian infection rates in the invaded range. Enemy release is likely to be more frequent when pathogens are rare in the home range, or are host specific and rare in reservoir populations of the introduced range.

Within any one habitat, the relative fitness of organisms in a population can vary substantially. Social insects like the common wasp are among the most successful invasive animals, but show enormous variation in nest size and other fitness‐related traits. Some of this variation may be caused by pathogens such as viruses that can have serious consequences in social insects, which range from reduced productivity to colony death. Both individual immune responses and colony‐level traits such as genetic diversity are likely to influence effects of pathogen infections on colony fitness. Here we investigate how infections with Kashmir Bee Virus (KBV), immune response and intracolony genetic diversity (due to queen polyandry) affect nest size in the invasive common wasp Vespula vulgaris. We show that KBV is highly prevalent in wasps and expression of antiviral immune genes is significantly increased with higher viral loads across individuals. Patriline membership within a nest did not influence KBV susceptibility or immune response. A permutational MANCOVA revealed that polyandry, viral load and expression of the immune gene Dicer were significant predictors of variation in nest size. High intracolony genetic diversity due to polyandry has previously been hypothesized to improve colony‐level resistance to parasites and pathogens. Consistent with this hypothesis, we observed genetically diverse colonies to be significantly larger and to produce more queens, although this effect was not driven by the pathogen we investigated. Invasive wasps clearly suffer from pathogens and expend resources, as indicated here by elevated immune gene expression, toward reducing pathogen‐impact on colony fitness.

When invasive species move to new environments they typically experience population bottlenecks that limit the probability that pathogens and parasites are also moved. The invasive species may thus be released from biotic interactions that can be a major source of density-dependent mortality, referred to as enemy release. We examined for evidence of enemy release in populations of the common wasp (Vespula vulgaris), which attains high densities and represents a major threat to biodiversity in its invaded range. Mass spectrometry proteomic methods were used to compare the microbial communities in wasp populations in the native (Belgium and England) and invaded range (Argentina and New Zealand). We found no evidence of enemy release, as the number of microbial taxa was similar in both the introduced and native range. However, some evidence of distinctiveness in the microbial communities was observed between countries. The pathogens observed were similar to a variety of taxa observed in honey bees. These taxa included Nosema, Paenibacillus, and Yersina spp. Genomic methods confirmed a diversity of Nosema spp., Actinobacteria, and the Deformed wing and Kashmir bee viruses. We also analysed published records of bacteria, viruses, nematodes and fungi from both V. vulgaris and the related invader V. germanica. Thirty-three different microorganism taxa have been associated with wasps including Kashmir bee virus and entomophagous fungi such as Aspergillus flavus. There was no evidence that the presence or absence of these microorganisms was dependent on region of wasp samples (i.e. their native or invaded range). Given the similarity of the wasp pathogen fauna to that from honey bees, the lack of enemy release in wasp populations is probably related to spill-over or spill-back from bees and other social insects. Social insects appear to form a reservoir of generalist parasites and pathogens, which makes the management of wasp and bee disease difficult.

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