Bioeconomic optimization of surveillance for detecting and eradicating quarantine forest pests and pathogens

Early detection is critical for effective responses to incursions of invasive species, making surveillance programs for potential invaders essential. As resources are limited, surveillance activities must be as effective and efficient as possible. We used a bioeconomic model to develop an optimal surveillance programme for six priority quarantine and two quarantine forest pests in Switzerland. We aimed to minimize costs of management (i.e., surveillance and eradication) for species that are mandated for eradication based on collaborative biosecurity agreements with the European Union. The model determined optimal surveillance effort, accounting for differences in introduction likelihood, detectability, and spread rates, across pests and locales. The model suggested a likely underestimate of optimal investment of 1,187,000 CHF per year for surveillance using visual surveys and insect or spore traps, depending on the target species. Survey recommendations varied across locales and pest types with the greatest surveillance effort for Agrilus planipennis, Bursaphelenchus xylophilus, Dendrolimus sibiricus, Fusarium circinatum, and Phytophthora ramorum. Surveillance trapping would be economically irrational for two pests (Anoplophora glabripennis, A. chinensis), primarily because of high probability of background detection by the public, and low efficacy of formal surveys and low spread rates. The model indicates where in Switzerland surveillance yields the highest economic return, with greater survey effort in areas with highest introduction risk and for species with low likelihoods of public detection and fast spread rates. The model indicates that the use of more effective trapping methods and an increase in public awareness could reduce the needed investments in formal surveillance activities.