Invasive species are globally significant drivers of species extinction. Invasive insects, such as Vespula wasps, are highly successful invaders with noted impacts on invertebrate communities. New Zealand beech forests, rich in honeydew and invertebrates, support Vespula wasps to reach some of the highest densities in the world. Having evolved without Vespula wasps for millions of years, New Zealand's indigenous invertebrates lack evolutionary experience to deal with predation pressures imposed by these wasps. New Zealand beech forests host numerous endemic invertebrates, including several lepidopteran species listed in the New Zealand Threat Classification System, that are potentially susceptible to wasp predation.

The beech forest butterfly, Dodonidia helmsii (forest ringlet butterfly), is the sole species in its genus. This species has experienced declines, range contractions, and extirpations from lower-altitude habitats, resulting in its threat classification of ‘At-Risk – Relict’. Changes in forest ringlet populations have been attributed to Vespula wasp invasion, but no research has been conducted to evaluate a potential predator-prey relationship. My research investigated the impacts of Vespula wasps on the forest ringlet using environmental surveys, predator exclusion methods, and DNA metabarcoding of wasp larval diet, in one of the known locations of the forest ringlet, the Kahurangi National Park.

I conducted environmental surveys to understand environmental variables associated with forest ringlet caterpillar detection. Surveys revealed that the extent of canopy cover above host plants had a substantial association with caterpillar detection. Other notable associations included the altitude of host plants, which was positively associated with caterpillar detections, and Vespula wasp detection, which was negatively associated with caterpillar detections.

To clarify the role of Vespula wasp and rat predation in potentially driving extirpations of forest ringlet populations in lower-altitude habitats, I translocated forest ringlet caterpillars to lower-altitude larval host plants. Using predator exclusion methods, I exposed translocated caterpillars to varying treatments of Vespula wasp and rat access and assessed caterpillar survival. Visual observations and trail camera footage identified wasps, rather than rats, as the likely predators responsible for the disappearance of seven translocated caterpillars.

I performed DNA metabarcoding on Vespula vulgaris larval meconium to look for evidence of predation of the forest ringlet. Additionally, I characterised the invertebrate diet of V. vulgaris wasps in a beech forest and evaluated inter- and intra-nest diet variability. Despite not detecting forest ringlet DNA in examined meconium, this research is the first to use DNA metabarcoding to characterise the diet of V. vulgaris in a beech forest. Findings included the identification of five new insect orders and 31 new families, not previously identified in the diet of V. vulgaris in a beech forest.

My research highlights the potential impact that Vespula wasps are having on forest ringlets in this locality, and it contributes to growing evidence that they have likely played a role in the extirpation of the forest ringlet from lower-altitude habitats. This research emphasises the need to strengthen wasp control in beech forests, not only to protect the forest ringlet butterfly but to protect other valued invertebrates also found in this ecosystem.