FinnSURV-Assess PWN is a tool for assessing the confidence in pest freedom gained in official pine wood nematode (PWN, Bursaphelenchus xylophilus ) surveys in areas where PWN is not expected to cause symptoms.
FinnSURV-Assess PWN can be used to assess both the sensitivity of annual surveys and the probability of freedom achieved in multiannual surveys.
The application assumes that a) the surveys are composed of inspections that cover a fixed sized area and b) in the inspections, one or more wood or Monochamus samples are collected. If all the needed data is provided separately for all regions of a country, the assessment is done separately for each region and for the whole country.
FinnSURV-Assess PWN automatically decides whether to assume sampling from finite or infinite population. If the sample size is always less than 10% of the total target population, the population is assumed to be infinite. Otherwise, the population is assumed to be finite.
The methodology used in the application is described in detail in Hannunen and Tuomola (2020) and references therein, especially Cannon (2002) , Martin et al. (2007) and Efsa (2012) .
To run the assessment with the parameters used in Hannunen and Tuomola (2020) , upload the csv files named in the popup help windows for the number of inspected sites (both for wood sampling and Monochamus trapping), the number of wood objects sampled per inspected site, the area with host plants and the area of entry sites. You can download the files here . For the other parameters, use the prefilled values.
Apparent prevalence = The proportion of samples testing positive
Design prevalence = Roughly, design prevalence determines the minimum prevalence that the survey is aimed to detect. If the pest prevalence is equal to or greater than the design prevalence, at least one infested individual will be detected in the survey, with the probability equal to the sensitivity of the survey.
Early detection survey = A survey that aims to detect possible PWN invasions early enough to enable successful eradication
Entry site = A site where the probability of PWN introduction is elevated, i.e. harbors, industrial areas and landfills
Import-export survey = A survey that aims to provide evidence to justify import requirements related to PWN and to facilitate export to countries with corresponding requirements
Initial prior probability of freedom = The probability that the prevalence of the pest is below the design prevalence before the first survey
Probability of freedom = The probability that the prevalence of the pest is below the design prevalence if the pest is not detected in the surveys
Sensitivity = Roughly, sensitivity determines the probability with which a survey is expected to succeed in its aim. If the pest prevalence is equal to or greater than the design prevalence, at least one infested individual will be detected in the survey, with the probability equal to the sensitivity of the survey.
Target population at the level of inspection site = Wood objects suitable for sampling / Monochamus adults
Target population at the level of regions = The area with PWN host plants in the area for which the results of the survey will be generalized
Test sensitivity = The probability that the pest is detected in the laboratory analysis, given that it was present in the wood object(s) / Monochamus beetle(s) included in the sample
The source code for FinnSURV-Assess PWN is published in Zenodo, https://zenodo.org/record/3842358 under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.
Hannunen S and Tuomola J 2020. FinnSURV-Assess PWN - A tool for assessing the confidence in pest freedom gained in official pine wood nematode surveys. Finnish Food Authority, Helsinki, Finland. Available at http://finnsurv-assess-pwn.rahtiapp.fi , https://doi.org/10.5281/zenodo.3842358