The measurement of parasitism rates of wasp nests;lt Pelorus Bridge, New Zealand, at different distances from the initial release point suggests that the mean displacement of the parasitoid has increased by 1—1.5 km y(-1) from 1988 to 1993. Since average parasitism rates within this radius at any given site show little trend over time, this suggests an approximate 3-fold increase in the total parasitoid population each year, two-thirds of which is devoted to dispersal and one-third to maintaining local populations.
Introduced common wasps (Vespula vulgaris) are widespread, abundant pests in New Zealand. They compete for food with native birds and feed on native invertebrates. We poisoned wasps annually over 4 years to see if it was possible to reduce their abundance in two 30-ha beech forest sites. Two different poisons (sodium monofluoroacetate and sulfluramid) were used, mixed with sardine catfood. There was no evidence that one poison was more effective than the other.
Honeydew, the sugary exudate of the scale insect Ultracoelostoma brittini, is an important food source in black beech (Nothofagus solandri var. solandri) forests in the South Island of New Zealand. Two of the most prominent foragers of honeydew are honey bees (Apis mellifera) and wasps (Vespula germanica and V. vulgaris). Observations in the field and using a captive bee hive were used to investigate competition between bees and wasps feeding on honeydew.
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.
Low acceptance of protein baits by common (Vespula vulgaris) and German (V. germanica) wasps (Hymenoptera: Vespidae) occurred after rain in honeydew beech forest. This corresponded with a sharp decrease in the proportion of natural protein in the diet of V. vulgaris and V. germanica, and a reduction in the concentration of carbohydrate-rich honeydew in the crops of foraging wasps carrying liquid.
In honeydew beech forest in the South Island of New Zealand, introduced Vespula vulgaris wasps are now very abundant. Approximated biomass estimates indicate that Vespula (mostly V. vulgaris) biomass (mean estimate at peak = 3761 g ha-1, averaged over the year = 1097 g ha-1) is as great as, or greater than combined biomasses of birds (best estimate = 206 g ha-1), rodents (up to 914 g ha-1 in some years, but usually much lower) and stoats (up to 30 g ha-1). Relative V.