The Difficulty of Reducing Introduced Wasp (vespula Vulgaris) Populations for Conservation Gains

New Zealand Journal of Ecology (1998) 22(1): 55-63 ©New Zealand Ecological Society offer any hope of reducing numbers to any great extent in the near future (Barlow, Moller and Beggs, 1996; Beggs, Harris and Read, 1996). Poison-baiting is currently the only viable technique for reducing wasp density, as finding and destroying nests is very labour intensive. Trials using poison-baiting have been carried out in relatively small sites (1.5 3 ha) (Spurr1991; 1993). Most of these trials measured poisoning success by monitoring individual colonies. An earlier trial site which attempted to reduce wasp abundance (measured by counting wasps in baited traps) by poison-baiting in a 7.2 ha was unsuccessful (Thomas et al. 1990). The reasons suggested were poor bait acceptance and reinvasion of workers from neighbouring areas. Given that the problems of reinvasion are likely to be smaller in larger areas, larger scale trials are required. Managers also need to know whether the costs and benefits of such an operation make it worthwhile. In 1991, we started a study to manipulate wasp numbers experimentally in two 30-ha sites to measure the impact of wasps on a beech forest community. This paper reports on the impact of 4 years of annual poisoning on wasp populations. Introduction