Guidelines for statistically sound and risk-based surveys of Phyllosticta citricarpa

At the request of the European Commission, EFSA prepared these specific guidelines to guide the surveyor through the design of statistically sound and risk-based surveys for Phyllosticta citricarpa, integrating the key biological information. Based on examples, three different survey designs are simulated: (i) detection surveys to substantiate pest freedom, (ii) delimiting surveys to determine the boundaries of an infested zone, and (iii) buffer zone surveys to monitor a zone ensuring pest detection at low levels of prevalence. The first step of the survey design consists of setting the goals of the survey, characterising the host plant population and the methods used to identify the pest. All survey parameters are quantified taking into account the importance of the related assumptions. The more accurate and robust the information used for selecting and estimating the survey parameters, the more robust the conclusions of the survey will be. The second step of the survey design consists of the sample size (i.e. number of trees) calculation using the survey parameters as inputs of the proposed statistical tool (EFSA RiBESS+). The last step of the survey design is the allocation of the samples in the survey area which depends on the information available on the target population and risk factors. The robustness of the conclusions of surveys designed using the proposed approaches strongly depends on the survey preparation. The methodology proposed allows surveys to be compared across time and space, thus contributing to the harmonisation of the P. citricarpa surveys across the EU. The extremely flexible approach allows the surveys to be tailored to each specific situation in the Member States, taking into account the citrus tree distribution and available resources. The success of a good survey design relies on the technical aspects of the survey preparation and on the involvement of the risk managers.