Improving wasp control by identifying likely causes of eradication failure

Studying the efficacy of control methods is paramount to successful management of invasive pests and understanding why some colonies survive is important to improve management practices. Here, the bait Vespex® was used to control invasive wasps across 64 ha of forest in an invaded range near Hanmer Springs, New Zealand. Bait was applied across a standard 50 m by 300 m arrangement and made available for 3 days. Nest mortality rates after 19 days were 29.8%, although nearly all nests were affected with a median overall reduction in nest traffic of 96.5%. The results from logistic regression showed that, all else remaining equal, larger wasp nests, nests further from bait stations, and more isolated nests exhibited lower rates of mortality after baiting. Investigating the change in activity at surviving nests, the results from beta regression suggest that declines in nest traffic were less severe with increasing distance to the nearest bait, but more severe with increasing nest size. These results indicate that while smaller nests are at a higher risk of being killed by the bait, they may not encounter bait as regularly as larger nests. Bait uptake varied considerably across bait stations. Wasp nests were not randomly or uniformly distributed in space, and instead were aggregated across our treatment area, likely due to some aspects of environmental conditions. We suggest further research to be focused on developing an understanding of the drivers of wasp nest development and foraging behaviour, to produce a more flexible baiting procedure that will increase both baiting efficiency and efficacy.