Prey Diets and Population-Densities of the Wasps Vespula vulgaris and Vespula germanica in Scrubland-Pasture

Prey collected by Vespula vulgaris and V. germanica were sampled by intercepting foragers returning to nests at two sites in scrubland-pasture near Hamilton. About 12% of returning foragers carried animal prey and 5% carried wood pulp. The remaining 83% carried no external load. The most common prey item for both species was Diptera, followed by Lepidoptera and Araneae (spiders). Even in similar habitats the two species collected different prey, with V. germanica collecting more Diptera and V. vulgaris more Lepidoptera. The prey changed slightly over time at both sites, V. germanica and V. vulgaris collected an estimated 1800 g and 600 g of prey nest-1 season-1 respectively. The wasps collected an estimated 75 000 prey loads ha-1 season-1 at Mystery Creek and 12 000 at Ruakura. This represents biomasses of 50 and 470 g ha-1, respectively, which are at least an order of magnitude lower than estimates of prey biomass for honeydew beech forest in parts of the South Island. The distribution of wasp nests was patchy however, and the biomass of prey collected exceeded 10 kg ha-1 in some places.