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Comparing the invasion success of the European paper wasp between the United States and South Africa

Background

Globalization has increased the frequency of species introduction and facilitated the spread of invasive species. Social wasps (e.g. hornets, yellowjackets, and paper wasps) are highly successful invasive species, capable of invading many diverse environments. In recent years, the rate of spread of invasive wasps has increased. Invasive social wasps often produce severe ecological and agricultural impacts. In some cases, populations can reach extreme densities and can dramatically alter native arthropod communities, resulting in biodiversity loss and ecological change. However, not every invasive wasp population is equally destructive. Some invasions form small, short-lived populations, with little impact to the local ecosystem. In contrast, other invasions are highly successful, reaching large, population sizes, and colonizing a range of different environments outside of their native distribution. Therefore, increasing our understanding of which factors are linked with invasion success is necessary for helping to combat invasive species and improving our ability to predict which invasive species are more likely to have the most harmful effects.

Many species of invasive social wasps have repeatedly invaded multiple regions, with varying results, providing a natural experiment to compare factors associated with invasion success. The native range of European paper wasp (Polistes dominula) (Figure 1) encompasses much of Europe and regions surrounding the Mediterranean. An invasive population of P. dominula was initially identified in Massachusetts in 1978. Within 20 years, this species had spread thousands of miles to California, rapidly adapting to novel environments, and negatively impacting the abundance of native paper wasp and butterfly species. Today, P. dominula occurs throughout the USA and Southern Canada and is the most common paper wasp species in urban environments.

Invasive populations of P. dominula have also been established in Australia (1980s), Chile (1980s), Argentina (2003), South Africa (2008), and New Zealand (2016) but in each of these cases, invasive populations have spread little from the initial invasion. In South Africa the invasion of P. dominula still currently occupies a very small geographic area of the Western Cape Province where it is largely limited to the greater Cape Town area and appears to have had little effect on native species density. Despite this small invasive range, populations of P. dominula quickly became very dense and by 2012 many Capetonians had encountered this wasp.

Objectives and outcomes

Funding from the program was used for two main objectives: (1) to develop new collaborative relationships between insect researchers at the ��ҹӰԺ St. Louis (UMSL), University of Western Cape (UWC), South African National Biodiversity Institute (SANBI), and Stellenbosch University (SU); and (2) to collect invasive European paper wasp samples from both Cape Town and St. Louis for DNA sequencing to estimate the location and size of the source population of these two invasions. Despite facing several unexpected challenges, we successfully achieved these objectives.

Developing new collaborations: the invasive social wasp network

To kick off this collaboration, there was a planned visit to Cape Town in March 2025 by Dr. Miller to meet with researchers at UWC, SANBI, and Stellenbosch University. Unfortunately, due to a last-minute family emergency, Dr. Miller had to cancel this trip and because of other commitments, could not reschedule.

Although we were not able to meet in person, we had many productive meetings online. Researchers at SANBI and SU have preexisting relationships with other social wasp researchers. Leveraging these connections, we organized a joint online brainstorming meeting between researchers across five different countries to discuss developing a larger global network of invasive social wasp biologists. As an outcome of this meeting, we decided to submit a collaborative research proposal to the National Science Foundation (NSF) and the National Research Foundation (NRF) of South Africa funding call, “Biodiversity on a Changing Planet”, to help formalize our invasive wasp network and quantify the impacts of invasive wasp population in different environments. This research proposal was led by PI Sara Miller from UMSL, along with Co-PIs Erin Rankin from the University of California – Riverside and Kevin Loope from Virginia Tech ($499,130). The South Africa Team included Ruan Veldtman from SANBI, Cang Hui and Barbara van Asch from Stellenbosch University, and Vanessa Couldridge from UWC (R700,000). Additionally, we had letters of support from colleagues in Argentina, and New Zealand. Unfortunately, due to an administrative error outside of the control of the PI or Co-PIs, this grant was not reviewed by NSF or NRF for this funding round. We planned on resubmitting this grant the following cycle, however recent changes in funding priorities at NSF resulted in the archiving of this funding opportunity. Currently, we are on the lookout for other funding to continue this collaboration. We also plan to discuss other opportunities for collaborations at the International Union for the Study for Social Insects (IUSSI) meeting in Frieberg Germany in August 2026.

Population genetics of the invasive European paper wasp

The initial scope of this project was to sequence specimens of P. dominula from South Africa and previously collected specimens from St. Louis and the surrounding regions. After writing the collaborative grant, I requested specimens from members of the invasive wasp network to increase the scope of the project. My lab received specimens of invasive P. dominula from South Africa that had been previously collected by researchers at SANBI; specimens from across the geographic range in the USA; and specimens from independent invasive populations in New Zealand and Argentina. Additionally, we received specimens from populations across most of the native range of this species. Together these samples will provide a much more cohesive overview of the source population for each invasive P. dominula population. Additionally, we will be able to look at difference in phenotype among populations, as well as get an idea of connectivity among populations. Due to the increased scope of this project, work is still ongoing. All specimens have been photographed and measured (Figure 2), and the first set of specimens have been sequenced. Data analysis is in progress, and a final manuscript is in preparation.

Products

• Established a wide network of invasive wasp researchers in both the USA and South Africa as well as globally.
• Collaborative partnership grant was jointly submitted to NSF and NRF
• Publication on European paper wasp invasive population genetics is in progress
• Dr. Miller will give an invited talk at the International Union for the Study for Social Insects (IUSSI) in Frieberg Germany in August 2026 on the results.

Conclusions

My prior research had focused primarily on native wasp species. This partnership program has given me the opportunity to expand my research program into invasive social wasps and has helped to facilitate connections between wasp researchers in the USA and in South Africa, and beyond. These connections have led to other collaborative opportunities that will be essential for tackling the challenging problems caused by invasive social insects. On the horizon is a visit to Cape Town and UWC by one of my PhD students through the Henry Mitchell fellowship program, with hopefully more opportunities to come in the future.