Explaining Vespula wasp population structure in the Hauraki Gulf
Invasive Vespula (common and German) wasps have a negative impact on the environment throughout New Zealand, preying on native invertebrates and competing with native nectar-feeding birds and invertebrates for the honeydew produced by native scale insects in beech forests. Both wasp species also inflict large economic costs on the farming, beekeeping, horticulture and forestry industries, and are a major nuisance to recreational users of wildlands. There has been renewed interest in managing these painful pests, with a New Zealand’s Biological Heritage National Science Challenge research programme to develop novel wasp suppression and eradication tools. The development of such tools requires an understanding of what factors limit or regulate wasp populations, a topic that PhD student Julia Schmack (University of Auckland) is investigating.
Julia’s supervisor, Jacqueline Beggs (University of Auckland), was intrigued by anecdotal reports that some islands in the Hauraki Gulf that had undergone mammal eradication programmes had subsequently become Vespula wasp-free. This was not thought to be due to non-target poisoning, since the toxin used to kill the mammals was applied in winter when wasps are inactive. Jacqueline realised that finding an ecological mechanism that limits or regulates wasp numbers could potentially be ‘leveraged’ for wasp control. Biologists have good understanding of the drivers of wasp population dynamics in beech forests, where Vespula wasps are hyper-abundant, but very little is known about what drives their presence and abundance in other habitats. Enter Julia, who is embarking on an intensive wasp survey of islands in the Hauraki Gulf.
Julia’s first objective is surveying as many islands as she can to determine wasp presence and abundance, assessing ecological characteristics such as island size, distance to the mainland or nearest neighbouring island, proportional cover of different vegetation types and presence of other fauna. By analysing this information, Julia hopes to identify which factors best explain wasp presence and abundance on offshore islands. Any relationship with mammal eradication will lead onto further work to identify a potential mechanism. Wasp presence or absence on particular islands might also be an outcome of meta-population processes. For example, wasps might go extinct on some islands but recolonise them the next year via queens from the mainland or nearby islands. Assigning wasps to their population of origin is therefore important for understanding reinvasion paths, and essential for the biosecurity management of offshore islands.
With this in mind, Julia is collecting samples of worker wasps from each island to take back to the laboratory for DNA extraction and genetic variability estimation. With the help of Phil Lester’s team (Victoria University), Julia aims to differentiate populations on different offshore islands and within mainland New Zealand, providing a biogeographical overview of the distribution and relatedness of Vespula wasp populations. If relatedness can be discriminated at the nest level there is also the potential to estimate wasp nest density; being able to do this without the time-consuming and often painful and dangerous effort of locating nests would be a huge advantage.
With spring underway, queen wasps are now emerging from their winter hibernation and Julia is gearing up for a big summer of fieldwork. She hopes to survey at least 10 islands this year. Unlike most people she is also hoping this summer will be a good year for wasps (summer 2016/17 was a low wasp year). Julia hopes her research into the drivers of wasp abundance on offshore islands will help identify a vulnerability that will lead to the development of better tools for large-scale wasp control, and thus contribute to the conservation of New Zealand’s unique ecosystems.
This work is funded by New Zealand’s Biological Heritage National Science Challenge
Mandy Barron (co-supervisor)
Jacqueline Beggs (University of Auckland)
Julia Schmack (University of Auckland)
Darren Ward (Manaaki Whenua - Landcare Research / University of Auckland)