Vespula foraging: implications for pollination and monitoring

Abstract

The impacts of invasive Vespula wasps are wide reaching, affecting biodiversity, ecosystem functions, primary industries, and human health and recreation. Minimal attention has been given to Vespula wasp populations in New Zealand’s non-honeydew beech forest habitats, despite the fact that honeydew beech forests have been well-examined. In addition, ecologists have given little consideration to potential impacts of Vespula wasps on New Zealand’s pollination networks. There are three main aims of this research: (i) to quantify differences in Vespula wasp population densities between non-honeydew beech forests and South Island honeydew beech forests; (ii) to develop a monitoring tool sensitive to low Vespula wasp abundance; and (iii) to evaluate the role of Vespula wasps within New Zealand’s pollination networks. Vespula wasp populations were sampled using Malaise traps in two native forest habitats in the Auckland region and two honeydew beech forest habitats in the South Island. A jar-lid count method was compared with sticky based Delta traps in order to develop a suitable method for measuring Vespula feeding activity in habitats with low wasp densities. The jar-lid count method proved ineffective, while Delta traps accumulated enough Vespula wasps to assess their relative abundance. Flowering plants visited by Vespula wasps in the Auckland region were identified and the facial hairiness and body pollen loads of Vespula wasps were determined to assess their potential as pollinators. Vespula wasps collected nectar from 22 plant species, of which 14 were native and 18 had open-access blossoms. Vespula wasps were, after ants, the second most abundant flower visitor to Metrosideros excelsa and interference competition was observed between Vespula wasps and other flower visitors. Facial hairiness and pollen loads of Vespula wasps suggest that they are poor pollinators, although high visitation rates may partly compensate for this. The following three findings of this research are the most significant. First, this research demonstrates that there is significant variation in the population density of Vespula wasps between honeydew beech forests and non-honeydew beech forests. Indeed, observed peak populations in non-honeydew beech forests were an order of magnitude lower than those in honeydew beech forests (2.8+0.76 and 58.0+5.10 wasps/trap/day, respectively). This is likely explained by the difference in sugar resources between the two habitats. Second, this research concludes that Delta traps baited with tuna are an appropriate tool for monitoring Vespula wasp feeding activity in habitats with low wasp densities, while lid-based counts are too insensitive to monitor low Vespula densities. Third, this research highlights the previously overlooked role of Vespula wasps in pollination networks: Vespula wasps may be significant flower visitors in habitats where floral nectar from open-access blossoms is a primary source of sugar. Overall, my research suggests that Vespula wasps, even though at much lower densities in non-honeydew beech forest than in honeydew beech forest, may be having ecological impacts that warrant both further research and management of this pest species.