Abstract
Biological invasions are one of the main driving factors of the current global biodiversity crisis. Out of all invasive species, social insects are some of the most widespread. In Aotearoa New Zealand, two species of Vespula are prolific invaders, the German wasp (Vespula germanica) and the common wasp (V. vulgaris). They reduce honeydew standing crop by over 90% for five months and suppress populations of invertebrates dramatically. Due to this domination of resources, mokomoko could be impacted by Vespula spp. by resource competition, and possibly predation. The key species in this study are two species of Naultinus, the Northland moko kākāriki (N. grayii) and the elegant moko kākāriki (N. elegans), both considered At Risk – Declining under national conservation assessment criteria. Moko kākāriki (green geckos, Naultinus spp.) are diurnal ectotherms, forage on invertebrates and sugar resources, are ambush predators and have a variety of predatory response behaviours. Anecdotal evidence suggests that Vespula spp. are a threat to moko kākāriki. Certain populations of moko kākāriki have been declining over the past 15+ years in areas of Aotearoa where Vespula spp. have their highest abundances. I investigated whether normal ‘maintenance’ behaviours and predator response behaviours of moko kākāriki were associated with Vespula wasp abundance or the time they spent in the vicinity of moko kākāriki. I undertook timed behavioural observations of captive moko kākāriki in a beech forest with variable wasp abundance, and five-minute wasp counts after each observation. I examined whether there was evidence of resource competition occurring between Vespula spp. and moko kākāriki, by using timelapse photography to investigate the foraging activity of moko kākāriki and Vespula wasps at a shared resource. I found little evidence suggesting that Vespula wasp abundance impacts the maintenance behaviours of moko kākāriki. However, they did elicit predator response behaviours such as freezing and dropping. Very infrequent direct interactions between geckos and wasps occurred during the observation periods, and thus results cannot rule out the possibility that Vespula spp. can impact moko kākāriki maintenance behaviour. I found evidence of potential resource competition occurring between Vespula spp. and moko kākāriki. Despite this, I believe that there is enough evidence to suggest that Vespula spp. are a threat to moko kākāriki, as the results of this study can only be applied to this system and cannot be generalised. Overall, this study is the first step in understanding the threat that Vespula spp. pose to moko kākāriki. There were some key limitations in this study, especially lower wasp abundance than usual for a season and reduced foraging of both moko kākāriki and Vespula wasps because it was an unseasonably cold and wet summer. My recommendation for future studies is to do a before and after landscape scale study with wasp poison baiting to evaluate potential benefits of wasp maintenance controlon moko kākāriki populations, with a control such as a BACI design. This study adds to a broader picture of how invasive Vespula spp. are impacting Aotearoa’s endemic taonga species, and how Vespula spp. are impacting mokomoko.