Many quarantine pests, such as the pine wood nematode (PWN, Bursaphelenchus xylophilus), are surveyed annually in all EU countries. Although a lot of resources are spent in the surveys, the confidence in pest freedom achieved with them is not commonly analysed. We assessed the probability that Finland is free from PWN, based on the surveys done in 2000–2018. We used the methods employed in the risk-based estimate of system sensitivity tool (RiBESS), which has recently been recommended for quarantine pest applications. We considered two scenarios: 1) the surveys aimed to justify phytosanitary import requirements and to facilitate exports and 2) the surveys aimed to detect invasions early to enable eradication of outbreaks. These differed only in the pest prevalence that the surveys were expected to detect. The surveys appeared to support the assumption that PWN is not present in Finland, but they did not seem extensive enough to ensure early detection of invasions. The sensitivity of the import-export surveys was greater than 0.6 in 13 years, whereas that of the early detection surveys was always below 0.25. The probability of freedom achieved in 2018 following 19 years of surveys increased asymptotically with the mean time between invasions. For the import-export surveys, this probability was at least 0.95 unless the mean time between invasions was less than 13 years. For the early detection surveys, the probability of freedom was less than 0.73 unless the mean time between invasions was 63 years or more. The results were rather robust with respect to the parameters for which exact information was lacking. To improve the assessment, a quantitative estimate of the probability of PWN invasion to Finland and a thorough assessment of the maximum area of an eradicable infestation would be needed. To gain an understanding about the true impact of quarantine pest surveys on biosecurity, more assessments, like the one presented in this paper, are needed.

中文翻译：

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根据19年的调查评估从松木线虫中获得自由的可能性

欧盟所有国家/地区每年都会调查许多检疫性有害生物，例如松木线虫（PWN，Bursaphelenchus xylophilus）。尽管在调查中花费了大量资源，但通常无法分析使用它们实现的对有害生物自由的信心。我们根据2000–2018年所做的调查，评估了芬兰摆脱PWN的可能性。我们使用了基于风险的系统敏感性工具（RiBESS）评估中所采用的方法，该方法最近被推荐用于检疫性有害生物的应用。我们考虑了两种情况：1）旨在证明植物检疫进口要求合理并促进出口的调查； 2）旨在及早发现入侵以根除疫情的调查。这些仅在预期调查发现的有害生物流行方面有所不同。这些调查似乎支持以下假设：芬兰不存在PWN，但似乎范围不够广泛，无法确保及早发现入侵。进出口调查的敏感度在13年中大于0.6，而早期发现调查的敏感度始终低于0.25。经过19年的调查，2018年实现的自由概率随着两次入侵之间的平均时间而逐渐增加。对于进出口调查，除非两次入侵之间的平均时间少于13年，否则该概率至少为0.95。对于早期发现调查，除非两次入侵之间的平均间隔为63年或更长时间，否则自由概率小于0.73。对于缺少准确信息的参数，结果相当可靠。为了改善评估，需要对PWN入侵芬兰的可能性进行定量评估，并彻底评估可根除的侵扰的最大面积。为了了解检疫性有害生物调查对生物安全性的真正影响，需要进行更多评估，如本文所述。