# Development and Evaluation of Preharvest Thaumatotibia leucotreta Citrus Fruit Infestation Monitoring for Inclusion in a Systems Approach

## TL;DR

This paper introduces a new method to monitor citrus fruit infestation by a pest in southern Africa, improving export safety and reliability.

## Contribution

A novel preharvest monitoring system using sanitation fruit sampling was developed and validated for pest risk mitigation.

## Key findings

- The new sanitation-fruit sampling method accurately reflects orchard infestation levels.
- A 100-fruit sample is sufficient for orchards up to 20 hectares.
- The new method is more reliable than the older fallen fruit inspection method.

## Abstract

The false codling moth is an important pest that can attack citrus fruit in southern Africa. Because this pest can infest fruit, it poses a threat to citrus exports, especially to countries with strict import rules. To reduce the risk of exporting infested fruit, farmers follow a “systems approach”, which includes several steps to keep pest levels low. One of these steps is checking for signs of the pest before harvest. This study looked at two ways of achieving this: an older method that involves checking fruit that have fallen from a few specific trees, and a new method that involves inspecting fruit collected during orchard clean-up. This research was carried out over two seasons, one with high pest levels and one with low levels. Both methods proved to be effective and acceptably accurate. The new method, which uses a sample of 100 fruit per orchard, was more reliable and worked well for orchards up to 20 hectares in size. These results support the use of the new method as part of the systems approach, helping growers reduce the risk of pest damage and maintain access to valuable international markets.

Thaumatotibia leucotreta, an important citrus pest in southern Africa, is subject to phytosanitary regulations for certain export markets. A systems approach has been developed as an alternative to standalone postharvest disinfestation methods, integrating multiple risk mitigation steps, including preharvest infestation monitoring. This study aimed to validate an existing preharvest monitoring protocol based on fallen fruit collected under designated data trees and to develop a novel monitoring system based on sampling of sanitation fruit. Monitoring was conducted in seven Navel orange orchards (N = 7 each year) during the 2021 and 2022 seasons, representing high and low infestation levels, respectively. Infestation levels were assessed over 11–12 weeks by inspecting fruit beneath four sets of five trees and all sanitation fruit collected per orchard. The new system, which involves inspecting a 100-fruit sample per orchard, was compared with the previous method. While the five-tree protocol tended to overestimate infestation, it remained effective. The sanitation-fruit sampling approach accurately reflected orchard-level infestation, with a 100-fruit sample sufficient for orchards as large as 20 hectares. Although random sampling is recommended, it was not essential for effectiveness. These results support the use of the new monitoring procedure in the systems approach for citrus exports for T. leucotreta risk mitigation.