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.
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.
Invasive species have an enormous global impact, with international trade being the leading pathway for their introduction. Current multinational trade deals under negotiation will dramatically change trading partnerships and pathways. These changes have considerable potential to influence biological invasions and global biodiversity. Using a database of 47 328 interceptions spanning 10 years, we demonstrate how development and governance socio-economic indicators of trading partners can predict exotic species interceptions. For import pathways associated with vegetable material, a significantly higher risk of exotic species interceptions was associated with countries that are poorly regulated, have more forest cover and have surprisingly low corruption. Corruption and indicators such as political stability or adherence to rule of law were important in vehicle or timber import pathways. These results will be of considerable value to policy makers, primarily by shifting quarantine procedures to focus on countries of high risk based on their socio-economic status. Further, using New Zealand as an example, we demonstrate how a ninefold reduction in incursions could be achieved if socio-economic indicators were used to select trade partners. International trade deals that ignore governance and development indicators may facilitate introductions and biodiversity loss. Development and governance within countries clearly have biodiversity implications beyond borders.
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