Predictive models for pest mortality

Cold treatment is a phytosanitary method that is commonly applied to manage cold sensitive, invasive pests that may be carried via the trade of agricultural commodities.

Cold treatment schedules establish mandated requirements for horticulture consignments to be held at a set temperature for a specified duration and typically aim to achieve a 99.99% mortality rate of the target pest. Development of cold treatment protocols rely on technical data from rigorous, large-scale laboratory experiments that must be repeated for each pest and fruit combination. These experiments involve significant financial investment and resources.

Fruit and vegetables are usually transported to markets in a cold supply chain to maintain the freshness and quality of the produce – but phytosanitary treatment schedules do not take into account how the commercial cool chain may reduce biosecurity risks by contributing to the cold-induced mortality of pests. 

To help address these challenges, we are working on a model that shows when the required “mortality threshold” is achieved during cold storage and transport in the cold supply chain. Insights from this model could inform the design of future market access arrangements that are more flexible and proportionate to risk. 

Modelling time-temperature dependent pest mortality in fruit

To inform our model, we analysed 28 publicly available cold treatment studies for cold-sensitive pests. The model is designed to predict the mortality of different pests over time, depending on key factors, including the type of pest (10 pest flies species), their developmental stage (e.g. eggs or larvae), exposed temperature (0-7 °C), and host fruit (13 fruit types).

Our model predicted shorter cold treatment durations compared to current protocols to reach the required “mortality threshold”. This suggests that existing schedules may be overly conservative. Maintaining produce at low temperatures for extended periods can increase storage costs, reduce product quality and shelf life, impacting commercial viability and profitability.

The model offers a powerful tool to optimise cold treatment requirements, potentially reducing time, cost, and impact on produce quality. By accurately estimating pest mortality across a variety of conditions, the model can be used to inform the design of more efficient and flexible treatment schedules that better align with commercial practices. This approach can significantly reduce the time and expense associated with developing new treatment schedules, provide flexibility to adapt to different pest-host combinations, and enhance the overall efficacy of quarantine measures. Looking ahead, this model could be adapted to guide phytosanitary risk management in a wider range of traded goods such as grains, seeds, and shipping containers.

To learn more about the model, read our paper in the Journal of Pest Science: