Establishment of the wasp parasitoid,Sphecophaga vesparum(Hymenoptera: Ichneumonidae), in New Zealand

Abstract

The parasitoid Sphecophaga vesparum (Hymenoptera: Ichneumonidae), has been released throughout New Zealand in an attempt to control introduced common (Vespula vulgaris) and German wasps (V. germanica) (Hymenoptera: Vespidae). The parasitoid overwintered and has probably become established at Pelorus Bridge, 25 km east of Nelson. In 1990, an infested nest was recovered 7.1 km from this release site, indicating that the parasitoid can disperse at least 2.37 km per year. However, the proportion of nests parasitised at Pelorus Bridge has increased only slightly in the first 3 years after release. No Sphecophaga were recovered from 1190 nests at 38 other sites where they were released and monitored. This may reflect the small number of parasitoids that emerged at some sites, the small number of nests inspected at others, or a low parasitoid population density. However, combined data from this and other studies suggests that the parasitoid is having difficulty in becoming established in many areas. It is still too early to assess whether the parasitoid will disperse widely, or reduce wasp numbers significantly where it does become established.