Social wasps are invasive in many regions around the world. In their new communities, introduced predators such as these wasps may be beneficial as consumers of exotic pests, but they will also consume native species. Here, we examined the diet of the exotic European paper wasp (Polistes dominula) and the closely related congener, Polistes chinensis, in a region of New Zealand where they co-occur. DNA barcoding was used to analyse their diet. The diet of both wasp species was largely Lepidopteran but other orders such as Hemiptera, Diptera and Coleoptera were also represented. Our analysis showed substantial site-to-site variation in diet. The two wasps differed significantly in their prey, although these differences appear to be driven by taxa identified from a small number of DNA reads in a small number of samples. Native and introduced fauna were represented in the diets of both wasps and included important agricultural pests. Of the 92 prey taxa able to be identified to species level, 81 were identified as exotic or introduced to New Zealand. The remaining 11 were species native to New Zealand. However, our estimates suggest over 50% of the prey DNA in the wasp diet is derived from native species. These wasps are abundant in some coastal and urban habitats, where they are likely to consume pest species as well as native species of conservation importance. The ecosystem services or costs and benefits provided by these invasive species are likely to be contingent on the prey communities and habitats they occupy.

1. The direct and indirect impacts that invasive predators have on communities within their invaded range are poorly understood, particularly in the early stages of invasion. Through top-down control of their prey, predators have the capacity to trigger cascading effects on lower trophic levels. 2. We found the recent arrival of the invasive paper wasp Polistes dominula Christ has been associated with substantial declines in local butterfly abundance in New Zealand. One of the butterfly species we observed to be affected is the monarch, Danaus plexippus Linnaeus with densities reduced by 66% at the study site. Field experiments were conducted to examine the strength of the predation pressure exerted by P. dominula on monarch caterpillars and the cascading effects on milkweed (Gomphocarpus physocarpus E. Mey.) fitness. 3. A survival study of monarch caterpillars was conducted across three habitat types (coastal, forest, and suburban). Caterpillar survival in suburban areas was lowest, with only 45% of caterpillars remaining after just 6 h of exposure to wasp foraging. Predation by P. dominula explained 85% of caterpillar deaths within the trial period. 4. The cascading effects of P. dominula presence were quantified through changes in the height, foliage, and reproductive output of milkweed plants. Monarch caterpillar predation by P. dominula was found to have a positive effect on milkweed fitness. 5. This study demonstrates a strong trophic cascade initiated by an invasive predator. These findings highlight the impacts an invasive species can have on local communities beyond their direct predatory effects.

Species distribution models (SDMs) are tools used by ecologists to help predict the spread of invasive species. Information provided by these models can help direct conservation and biosecurity efforts by highlighting areas likely to contain species of interest. In this study, two models were created to investigate the potential range expansion of Polistes dominula Christ (Hymenoptera: Vespidae) in the southern hemisphere. This palearctic species has spread to invade North and South America, South Africa, Australia, and more recently New Zealand. Using the BIOCLIM and MAXENT modelling methods, regions that were suitable for P. dominula were identified based on climate data across four regions in the southern hemisphere. In South America areas of central Chile, eastern Argentina, parts of Uruguay, and southern Brazil were identified as climatically suitable for the establishment of P. dominula. Similarly, southern parts of South Africa and Australia were identified by the model to be suitable as well as much of the North Island and east of the South Island of New Zealand. Based on outputs from both models, significant range expansion by P. dominula is possible across its more southern invaded ranges.

We examined the abundance, nesting ecology, and colony survival of two invasive species of paper wasp, Polistes dominula Christ (Hymenoptera: Vespidae) and Polistes chinensis Pérez (Hymenoptera: Vespidae), within their invaded range in New Zealand. The more recent invader, P. dominula, exhibited a strong habitat preference, reaching the highest abundances within suburban areas with an average of 87.4 wasps per 1,000 m2. Coastal habitats were also found to be suitable environments for P. dominula, although wasp abundance in these areas was comparatively lower than suburban sites at 26.5 wasps per 1,000 m2. Although P. chinensis were observed to build more nests in coastal habitats, this was not reflected in the abundance of adult wasps in these areas. Nests of P. dominula were larger and more productive, likely a result of the multiple founding and earlier emergence of workers compared to P. chinensis. Both species exhibited significant differences in nest survival, with P. dominula observed to have a higher colony survival rate, particularly in suburban habitats where this species utilized man-made substrates as nesting sites. Neither species nested within forest sites and translocated nests of P. dominula failed to thrive within forest habitats. Findings of this research suggest that P. dominula will not pose a threat to species inhabiting forested areas. Instead, biodiversity managers should focus their efforts on suburban and coastal environments as native species in these areas will require the greatest protection.

Social insects are successful and globally significant invaders. Compared to ongoing suppression, eradication is seen as an ideal solution and cost effective in the long term. The success of eradication attempts is not guaranteed and identifying key factors that could influence the success of such management programs would be beneficial. In this study, 239 eradication attempts were compiled and analysed to identify why eradication attempts fail, with a focus on how eusociality of the target species impacts eradication success. All else remaining constant, the odds of successful eradication were 79% lower when targeting social species compared to non-social insects. Eradication success was shown to increase when comparing more recent attempts to earlier ones but was found to decrease as the duration of the attempt went on. Eradication attempts that occurred on islands, and those that targeted species with a broader host range, were also associated with increased success. A review of cited reasons for eradication failure highlighted the importance of employing effective control treatments, management, and monitoring systems, as well as garnering adequate social and political support. This study indicates how social insects are particularly challenging to eradicate; it also notes the importance of considering both logistical and biological aspects of any eradication, before initiating eradication attempts.