Model of the probability of pest transfer to a site suitable for establishment following their arrival on imported fruit, cut-flower or vegetable produce

Abstract

A model was developed to improve pest risk assessments and to better advise risk managers and policy makers on the relative importance of the pathways of pest entry and the strength of measures to be taken on each. The model computes the probability of the transfer of insect or mite pests from traded commodities to hosts at sites suitable for establishment. The probability is calculated from arrival of the pest on imported produce (cut flowers/branches, fruits or vegetables), up-to-and-including first egg laying, and taking into account any necessary development of the pest to a suitably mobile stage. Three case studies, Helicoverpa armigera on Rosa cut flowers, Thrips palmi on Solanum fruit and Rhagoletis mendax on Vaccinium fruit, are explained in detail. Probabilities were estimated for nine variables from which a joint probability, the probability of transfer, was calculated for each of the species–product combinations and trade chain scenarios. Although the probabilities were expressions of expert belief, rather than empirically derived, the resulting large differences in outcomes between the cases gave greater discrimination of relative risk than more qualitative approaches. The model helps to identify pest and trade-chain characteristics that are most limiting to transfer and so highlights the importance of these characteristics for future assessments. For pests that arrive as immature stages that are relatively immobile, development into an adult was identified as an important limiting factor especially for pests with a long lifecycle in relation to the shelf life of the product. For pests that have a limited dispersal ability the proximity to a suitable site was an important factor. Pests that arrive as adults, or can rapidly attain adulthood, and that can establish close to the destination of the produce are therefore a particular biosecurity concern.