Better colony performance, not natural enemy release, explains numerical dominance of the exotic Polistes dominula wasp over a native congener in South Africa

The European paper wasp Polistes dominula has invaded many parts of the globe and often displaces similar native species. Factors contributing to this remain unclear but may include longer seasonal activity period, natural enemy release, greater colony productivity and smaller body size. Since its discovery in South Africa in 2008, the local abundance of P. dominula has increased greatly. In invaded habitats, it is now much more common than the native P. marginalis. Here we determine some of the factors that enable dominance of P. dominula over the native congener during early stages of the invasion process. The activity of both species was monitored in four habitat types (urban, rural, fringe and natural) to determine differences in abundance, seasonal activity period, and habitat preference. Nests and individuals of both species were collected and compared for colony productivity (nest size), parasitism levels, and size of individuals. Both species preferred anthropogenically altered habitats, with P. dominula significantly more abundant than P. marginalis. Contrary to expectation, the exotic species suffered significantly higher parasitism than the native species. However, P. dominula had a substantially longer activity period and greater colony productivity than P. marginalis. P. dominula is therefore able to reach much greater population size than P. marginalis despite higher parasitoid pressure and similar individual size due to better colony performance. This has implications for future biological control initiatives.