# Inferring fruit infestation prevalence from a combination of pre-harvest monitoring and consignment sampling data

## TL;DR

This paper introduces a method to estimate fruit infestation rates by combining pre-harvest monitoring and consignment sampling data using a Bayesian model.

## Contribution

A hierarchical Bayesian model is developed to integrate in-field and consignment data for infestation prevalence estimation.

## Key findings

- Pre-harvest monitoring with sufficient trap density can provide 95% belief in very low infestation prevalence.
- High inspection sensitivity and multiple consignment samples can confirm low infestation rates without pre-harvest data.
- The model accounts for uncertainty in inspection and monitoring methods.

## Abstract

International trade in horticultural produce happens under phytosanitary inspection and production protocols. Fruit inspection typically involves the sampling and inspection of either 600-pieces or 2% of packed product within a single consignment destined for export, with the purpose of certification (typically with 95% confidence) that the true infestation level within the consignment in question doesn’t exceed a pre-specified design prevalence. Sampling of multiple consignments from multiple production blocks in conjunction with pre-harvest monitoring for pests can be used to provide additional inference on the prevalence of infested fruit within an overall production system subject to similar protocols. Here we develop a hierarchical Bayesian model that combines in-field monitoring data with consignment sample inspection data to infer the prevalence of infested fruit in a production system. The results illustrate how infestation prevalence is influenced by the number of consignments inspected, the detection efficacy of consignment sampling, and in-field monitoring effort and sensitivity. Uncertainty in inspection performance, monitoring methods, and exposure of fruit to pests is accommodated using statistical priors within a Bayesian modelling framework. We demonstrate that pre-harvest surveillance with a sufficient density of traps and moderate detection sensitivity can provide 95% belief that the prevalence of infestation is below \documentclass[12pt]{minimal}
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\begin{document}$$1 \times 10^{-6}$$\end{document}1×10-6. In the absence of pre-harvest monitoring, it is still possible to gain high confidence in a very low prevalence of infestation (\documentclass[12pt]{minimal}
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\begin{document}$$<1 \times 10^{-5}$$\end{document}<1×10-5) on the basis of multiple clean samples if the inspection sensitivity during consignment sampling is high and sufficient consignments are inspected. Our work illustrates the cumulative power of in-field surveillance and consignment sampling to update estimates of infestation prevalence.