Poles Apart: Comparing Trends of Alien Hymenoptera in New Zealand with Europe (DAISIE)

Developing generalisations of invasive species is an important part of invasion biology. However, trends and generalisations from one part of the world may not necessarily hold elsewhere. We present the first inventory and analysis of all Hymenoptera alien to New Zealand, and compare patterns from New Zealand with those previously published from Europe (DAISIE). Between the two regions there was broad correlation between families with the highest number of alien species (Braconidae, Encyrtidae, Pteromalidae, Eulophidae, Formicidae, Aphelinidae). However, major differences also existed. The number of species alien to New Zealand is higher than for Europe (334 vs 286), and major differences include: i) the much lower proportion of intentionally released species in New Zealand (21% vs 63% in Europe); and ii) the greater proportion of unintentionally introduced parasitoids in New Zealand (71.2% vs 22.6%). The disharmonic 'island' nature of New Zealand is shown, as a high proportion of families (36%) have no native representatives, and alien species also represent >10% of the native fauna for many other families. A much larger proportion of alien species are found in urban areas in New Zealand (60%) compared to Europe (similar to 30%), and higher numbers of alien species were present earlier in New Zealand (especially <1950). Differences in the origins of alien species were also apparent. Unlike Europe, the New Zealand data reveals a change in the origins of alien species over time, with an increasing dominance of alien species from Australasia (a regional neighbour) during the past 25 years. We recommend that further effort be made towards the formation, and analysis, of regional inventories of alien species. This will allow a wider range of taxa and regions to be examined for generalisations, and help assess and prioritise the risk posed by certain taxa towards the economy or environment.