New molecular technologies to improve the Sterile Insect Technique for the Mediterranean fruitfly Ceratitis capitata (Diptera; Tephritidae)

Insect pests cause enormous economic losses to livestock as well as pre- and postharvest stages of agricultural commodities. The Mediterranean fruit fly Ceratitis capitata (medfly; Wiedemann, Diptera: Tephritidae;) is one of the world's most destructive and invasive pest species, costing farmers billions of dollars annually. Insecticides have been used extensively during the last century and are still used to control C. capitata and other insect pests. However, to reduce the amount of insecticides and to increase the species-specificity of pest control, the existing tactics have to be improved. During the last decades biological approaches opened up new possibilities for insect pest management. Of these, the ecologically safe Sterile Insect Technique (SIT) developed into a powerful method for area-wide pest control. The SIT reduces the pest population by mass release of radiation-sterilized organisms, leading to infertile matings and in consequence to a decline of the pest population. Male-only releases proved to be most effective for medfly SIT programs. An SIT program for medfly includes mass-rearing, sex-separation for male-only releases, marking for monitoring, sterilization, releasing, and monitoring of male flies. Although the SIT is already successfully applied for medfly, each of these steps needs to be improved to optimize the efficiency and to reduce the costs of ongoing medfly SIT programs. Here, I present the development of several transgenic systems to improve the steps of sterilization, sex-separation, marking, and monitoring in medfly SIT programs. First, molecular methods to isolate developmental genes were successfully practiced in Tephritid fruit flies. Second, a transgenic embryonic lethality system was established and successfully evaluated in medfly to achieve reproductive sterility without the need for radiation. Third, this system has been further modified to design a female-specific embryonic lethality system, which is intended to improve sex-separation. Fourth, two sperm marking systems were established and successfully evaluated to improve the marking and monitoring of medfly. The male-specific transgenic fluorescent markers can replace the currently used problematic dust markers in monitoring and the systems will help to increase the knowledge about reproductive biology of the polyandrous medfly. Fifth, a system was designed that makes it possible to combine or modify transgenic systems at successfully evaluated genomic sites. This can be used to stabilize transgenes and further improve the generation of transgenic medfly systems for insect pest control. I anticipate that several of the transgenic systems developed in this study and combinations thereof will increase the efficiency of the environmental-friendly SIT.