Effective distances of wasp (Vespula vulgaris) poisoning using clustered bait stations in beech forest

Poison baiting from fixed bait stations is currently the most effective method to reduce the ecological impacts of invasive Vespula vulgaris wasps in New Zealand. Maintaining extensive bait lines or grids and later removal of unused baits within forest habitats is, however, difficult and time-consuming. To improve cost-effectiveness and to make use of wasps’ ability to forage at long distances from the nest, we tested the efficacy of using clusters of bait stations. We set up three clusters around Lake Rotoiti within Nelson Lakes National Park, each containing eight stations baited with Xtinguish^TM (active ingredient 0.1% fipronil) for 3–4 days in early February, 2010 and recorded the traffic rates of 144 V. vulgaris nests, at varying distances from bait clusters, before and after treatment. The distance from a bait station cluster significantly affected the change in traffic rates, with a GLM model predicting an 80% reduction in average colony size within 113 m of a cluster, and a 50% reduction within 250 m but no reduction at 470 m. The efficacy of the poison baiting was affected by initial colony size – large colonies had greater reductions in traffic than small colonies. Nests up to 150 m higher in elevation than the clusters were as likely to be destroyed as those at the same elevation as the clusters. While overall this baiting strategy did not produce the 80–90% average traffic reductions achieved by more intensive grid baiting systems, it suggests that spacing grouped bait stations approximately 250 m apart has the potential to reduce wasp densities to below an ecologically damaging level with considerably less effort.