Influence of overflooding ratios on fruit damage and population growth of Thaumatotibia leucotreta (Meyrick): implications for the sterile insect technique program.

Background: Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a significant pest of citrus in South Africa. A key management strategy to control this pest is the sterile insect technique, which relies on releasing high numbers of sterile T. leucotreta in citrus orchards. The study investigated different release ratios of newly emerged sterile to fertile T. leucotreta adults (0:1, 10:1, 20:1, 40:1, 60:1), which were placed in insect-rearing cages and allowed to mate. After 4 weeks, the number of damaged fruit and larval entries per fruit were recorded. Infested fruits were incubated until all emerging F1 progeny were collected.

Results: The cages with sterile T. leucotreta had significantly fewer infested fruits, larval entries, and F1 adults compared to the control. There was a negative correlation between the number of infested fruits, larval entries, and F1 adults with increasing ratios of sterile T. leucotreta. Control cages exhibited higher fecundity and fertility compared to treatment cages. The 40:1 and 60:1 treatment ratios showed the lowest per generation rate of increase (<1× from the parental to the F1 generation).

Conclusion: The study demonstrated that the 40:1 and 60:1 ratios were particularly effective, indicating that maintaining this ratio could significantly reduce the growth of the T. leucotreta fertile population, relative to lower ratios, albeit still effective. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.