Improving current wasp management towards eradication

Social insects are successful and globally significant invaders. Compared to ongoing suppression, eradication is seen as an ideal solution and cost-effective in the long term. Wasp eradication is a worthy target but with current technologies and approaches it may be a difficult one to achieve. In this thesis, I analysed both past and present approaches to invasive species management to identify ways to improve our current wasp management toward the goal of nationwide eradication of invasive social wasps in Aotearoa New Zealand.

The success of eradication attempts is not guaranteed and identifying key factors that could influence the success of such management programs would be beneficial. In Chapter 2, I analysed 239 historical and recent insect eradication attempts to identify predictors of eradication failure. I found that sociality is a significant predictor of eradication failure. The data suggested that more recent eradication attempts experience higher rates of success but that the increasing duration of a program is associated with reduced odds of success. The target species' host range and the geographic setting of the invasion were also found to be significant. Cited reasons for eradication failure highlighted the importance of effective control methods, management, and monitoring systems, as well as garnering adequate social and political support. Social acceptance and support for pest management programs are essential to success. In Chapter 3, I spoke to local stakeholders to explore their perceptions of current wasp management and what attempting eradication means for them. I interviewed 13 local stakeholders involved in 7 pest management projects across Aotearoa New Zealand. Q-method analysis identified two major perspectives across the participants. An ambitious perspective emerged where eradication of wasps was the target, and any control method deemed effective could be used to achieve that goal. The second perspective identified agreed that wasps must be managed but were characterised as more holistically minded and less accepting of control methods perceived to have negative impacts or side effects. Education and engagement were highlighted as essential to increase local support for future wasp management. Emphasis not just on technical but social and cultural aspects of wasp eradication is key to management success.

Effective control methods are paramount to successful pest management of invasive pests. Understanding why some treatments fail is important to improve management practices. In Chapter 4, I investigated how a common wasp control method could be improved to maximise wasp control. The toxic bait Vespex® was used to control invasive wasps across 64ha of forest near Hanmer Springs, Aotearoa New Zealand. The median reduction in nest traffic at treatment nests was 96.5%. Logistic regression analysis suggests that larger wasp nests, nests further from bait stations, and more isolated nests exhibited lower rates of mortality after baiting. At surviving nests, beta regression analysis suggested that declines in nest traffic were less severe with increasing distance to the nearest bait, but more severe with increasing nest size. Bait uptake varied considerably across bait stations and wasp nests were spatially aggregated, both likely due to aspects of environmental conditions.

Understanding and considering potential unintended negative consequences of pest management is critical when attempting eradication. In Chapter 5, I investigated the potential negative impacts of toxic baits used widely in current invasive wasp management on a non-target species the Wellington tree wētā (Hemideina crassidens). In laboratory settings, wētā exposed to bait containing the active ingredient fipronil at all concentrations (0.1%, 0.01%, and 0.001% by mass respectively) experienced significantly higher rates of mortality (70%-90%) compared to control baits (10%) after 2 weeks. A follow-up field study looked to investigate how bait presence may impact wētā survival in a more realistic baiting scenario. Wētā box occupancy was monitored over the course of a simulated wasp baiting program at two forest sites, with bait stations placed within 30cm of half of the boxes. Analysis showed that wētā box occupancy was not significantly affected by bait presence. Additional research will be needed to truly estimate the impact of current wasp management on wētā populations though simple steps may be taken to reduce nontarget effect. In this thesis, I show that social insects are particularly challenging to eradicate. Before undertaking any eradication attempt it is important to consider both logistical and biological aspects of managing a species incursion. Ensuring pest management actions are supported by local stakeholders is critical to project success. Engagement and collaboration are needed to develop effective pest management programs. Research conducted here identifies avenues to improve current management techniques to increase efficiency and efficacy while reducing non-target impacts. These improvements would serve to increase the chance of eradication success by more effectively reducing pest populations but also increasing the social acceptance of the program.