Invasive wasps, not birds, dominate in a temperate honeydew system

The Avian Convergence Hypothesis states that avianhoneydew associations are likely to develop when biogeographic and/or climatic factors limit the formation of anthoneydew associations (the dominant association in tropical ecosystems). In this study we examine a honeydew-influenced forest system in an island archipelago where ant diversity is low but invasive Vespula wasp species (Vespidae) are present. We found honeydew production was highly seasonal, with both standing crop and 24-h production peaking in summer. When Vespula wasps were abundant (summer and autumn) they preferentially visited infested trees and fed regularly on honeydew droplets on infested branches. Two ant species occasionally fed on honeydew. No other insects or birds were observed feeding on honeydew during the study period. With the exception of Vespula, honeydew does not appear to be a preferred food source in this community, possibly because of the range of other food resources available in surrounding forest, farmland and gardens. The abundance of Vespula wasps at the site may also have disrupted birdhoneydew associations. We suggest the Avian Convergence Hypothesis could be restated to explicitly include both nectar availability and invasive social insects as both are likely to influence bird use of honeydew.