Chemical ecology of invasive social wasps in New Zealand

Vespula wasps are invasive alien species throughout much of the Pacific that have severely impacted the food web in the beech forests (Nothofagus spp.) of New Zealand???s South Island. Understanding the types of cues and/or attractants that wasps respond to may foster the development of novel control tools. Few studies have been made regarding sex attraction behaviour of V. vulgaris and V. germanica. Here, both species of wasps were shown to use a gyne produced sex pheromone to attract males under wind tunnel and field conditions. Significant numbers of males were caught in delta traps baited with live caged gynes, while no gynes were caught in traps baited with males. A small but significant degree of cross-species sex attraction was found to occur in both laboratory and field experiments. During laboratory mating trials, there was an initial attraction by the males to gynes of the other species, but they lost interest very rapidly without attempting to mount the gyne. No interspecies mating took place during the experiments. From the chemical analysis of the cuticular hydrocarbons from the gasters of gynes, I identified 17 cuticular hydrocarbons that both V. vulgaris and V. germanica had in common, although in different proportions. Multivariate analysis of the hydrocarbon compounds was able to demonstrate to which species the hydrocarons belonged. To dertmine this with 100% accuracy as few as five compounds were all that was needed. While there have been many studies investigating the impacts that invasive Vespula have had on the honeydew beech forest ecosystem, no studies have looked at the chemical cues that the wasps are using to locate honeydew. Volatile collections were taken from black beech tree trunks with honeydew and sooty mould present and analysed with a gas chromatograph-mass spectrometer (GC-MS). Eleven compounds were positively identified and were shown to elicit an electrophysiological response from V. vulgaris worker antennae using an electroantennogram (EAG). Field trials confirmed wasp attraction to nine of the eleven compounds and to the corresponding two blends, tested using delta traps baited with individual compounds. A field trial showed raw fermented brown sugar solution to be attractive to wasps. Ten chemical compounds were identified from fermented brown sugar solution headspace using GC-MS and confirmed with synthetic references. Field trapping confirmed that at least three of these compounds were highly attractive to Vespula wasps at beech forest margins. Together, these discoveries have the potential to lead to novel controls of invasive wasps in New Zealand.