Feasibility of eradicating the large white butterfly (Pieris brassicae) from New Zealand: data gathering to inform decisions about the feasibility of eradication

Pieris brassicae, large white butterfly, was first found in New Zealand in Nelson in May 2010. The Ministry for Primary Industries (MPI) responded with a monitoring programme until November 2012 when the Department of Conservation (DOC) commenced an eradication programme. DOC was highly motivated to eradicate P. brassicae by the risk it posed to New Zealand endemic cress species, some of which are already nearly extinct. DOC eliminated the butterfly from Nelson in less than four years at a cost of ca. NZ$5 million. This is the first time globally that a butterfly has been purposefully eradicated. Variation in estimates of benefits, costs, the efficacy of detection and control tools, and the probability of eradication success all contributed to uncertainty about the feasibility. Cost benefit analyses can contribute to assessing feasibility but are prone to inaccurate assumptions when data are limited, and other feasibility questions are equally important in considering the best course of action. Uncertainty does not equate to risk and reducing uncertainty through data gathering can inform feasibility and decision making while increasing the probability of eradication success.