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

Abstract

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.