Effects of Different Combinations of Sterile and Fertile Thaumatotibia leucotreta on Fruit Infestation and Population Growth Rate

Abstract

Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a key phytosanitary pest of citrus in South Africa. The pest damages fruit by burrowing and feeding on the pulp, thus causing yield losses and export rejections. There are several T. leucotreta management strategies, such as orchard sanitation, mating disruption, attract-and-kill, the use of biocontrol agents, and the sterile insect technique. A laboratory cage study was conducted to examine the impact of different combinations of treated (sterile) and untreated (fertile) T. leucotreta adults on fruit damage and reproduction rate. Thaumatotibia leucotreta adults were grouped into different combinations of treated (T) and untreated (U) male (M) and female (F): UM × UF (control), TM × UF, UM × TF, TM × TF, and UM × UF × TM × TF. These combinations were released into cages to mate and oviposit on the Navel oranges. Each treatment was replicated three times, and the experiment was repeated three times. After 4 weeks, the number of damaged fruit and larval entries per fruit per cage were recorded. Damaged fruit per treatment were then incubated until all emerging F1 progeny were collected and outcrossed with fertile T. leucotreta. Fecundity and fertility per treatment were recorded. Cages with sterile T. leucotreta had significantly fewer damaged fruit, larval entries, and emerged F1 adults compared to the control, except for UM × UF × TM × TF treatments. Similarly, control cages and UM × UF × TM × TF treatments had significantly higher fecundity and fertility compared to other treatments involving sterile T. leucotreta. The TM × UF combination exhibited the lowest rate of increase per generation (< 0.57× from the parental to F1 generation), demonstrating a reduction in the fertile population. The results demonstrated that the release of sterile T. leucotreta leads to sterile-fertile matings rather than fertile-fertile matings, thereby aiding in pest suppression in the T. leucotreta SIT programme.