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.

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.

<p><b>Introduced wasps can have significant impacts on communities within their newly invaded range. A recent wasp introduction to New Zealand is the European paper wasp, Polistes dominula Christ, which was first observed in the Nelson-Tasman region in 2016. The ecology and behaviour of P. dominula was investigated, as well as the direct and indirect impacts of this wasp on local communities in Nelson. Aspects of nesting behaviour, habitat preference and abundance were studied with the intent to inform management decisions. The abundance and colony survival of P. dominula was greatest in suburban areas, where nests were predominantly built within anthropogenic structures. Colony survival of P. dominula was comparatively higher than for colonies of the longer established exotic congener Polistes chinensis Pérez. Neither Polistes species were found to nest within native or exotic forest sites, with translocated colonies of P. dominula unsuccessful within forest habitats. As a species that originates from a warmer climate, the lower temperatures in forests are likely a contributor to the inability of P. dominula to thrive in these areas. </b></p><p>The impacts that newly invasive predators have on communities within their invaded range are often poorly understood. Following the arrival of P. dominula, I show data indicating that there have been substantial declines in the abundance of several local butterfly species in Nelson. The monarch butterfly, Danaus plexippus Linnaeus was one of the species reported by residents to be in population decline. Field experiments found P. dominula to be a major cause of monarch caterpillar mortality. Caterpillar survival was the lowest in suburban areas, where the abundance of P. dominula was highest. Early instar caterpillars had comparatively higher mortality rates than late instar caterpillars, as the defensive behaviour of larger caterpillars had greater success against these wasps. Whilst P. dominula was the main driver behind caterpillar mortality throughout my experiments, the discovery of caterpillars by wasps appeared to happen by chance through direct contact between the wasp and their prey. There was also no evidence of nestmate recruitment by foraging wasps to sites where caterpillars were found. </p><p>Predation has the capacity to not only impact prey populations, but through the suppression of herbivory, plants can indirectly benefit from the presence of predators. The presence of P. dominula was found to have strong, cascading effects on the milkweed host and food plant of D. plexippus. Milkweed fitness in areas populated by P. dominula was substantially greater than the fitness of plants in areas without this invasive predator. Plant growth and reproduction of milkweeds placed in areas where P. dominula were present, and able to predate upon caterpillars, were found to exhibit a similar amount of growth and flower production as netted control plants which excluded monarch caterpillars completely. The outcomes of this experiment suggest that P. dominula is strongly suppressing these herbivorous caterpillars. </p><p>Overall, this thesis provides insight into the behaviour and ecology of P. dominula in New Zealand. Findings of this research suggest that this newly invasive wasp is having detrimental effects on local communities and that P. dominula should be controlled to reduce the impacts of this wasp on New Zealand’s ecosystems. Knowledge obtained in this study can direct conservation management strategies and aid in the development of effective control methods. </p>

Invasive paper wasps such as Polistes dominula are a major pest and problem for biodiversity around the globe. Safe and highly targeted methods for the control of these and other social wasp populations are needed. We attempted to identify potentially-lethal gene targets that could be used on adult paper wasps in a gene silencing or RNA interference (RNAi) approach. Double-stranded RNA (dsRNA) was designed to target genes for which silencing has proven lethal in other insects. dsRNA was provided either orally to foragers or directly injected into the wasps. We also provided the dsRNA unprotected or protected from degradation by gut nucleases in two different forms (lipofectamine and carbon quantum dots). The effects of oral delivery of 22 different gene targets to forager wasps was evaluated. The expression of five different genes was successfully reduced following dsRNA ingestion or injection. These gene targets included the FACT complex subunit spt16 (DRE4) and RNA-binding protein fusilli (FUSILLI), both of which have been previously shown to have potential as lethal targets for pest control in other insects. However, we found no evidence of significant increases in adult wasp mortality following ingestion or injection of dsRNA for these genes when compared with control treatments in our experiments. The methods we used to protect the dsRNA from digestive degradation altered gene expression but similarly did not influence wasp mortality. Our results indicate that while many of the same gene targets can be silenced and induce mortality in other insects, dsRNA and RNAi approaches may not be useful for paper wasp control.