The traits that determine male reproductive success in Ceratitis capitata (medfly) are largely unknown. This comes despite decades of research into the reproductive behaviour of this agricultural pest. An understanding of what makes a successful male is of great importance in this lekking species, as one male has the ability to dominate access to females. In addition species-specific pest control techniques such as the Sterile Insect Technique (SIT) and Release of Insects carrying a Dominant Lethal (RIDL) rely on the mating competitiveness of mass-reared ‘sterile’ males to disrupt natural mating systems and reduce population numbers. However, it is well known that the mass-rearing process required to generate these individuals produces less competitive males, despite this an understanding of the sexual selection processes that are involved is severely lacking. In this thesis I used the medfly as a model organism to investigate the context-dependent nature of male reproductive success. In Chapters 2 and 3 I investigate the effect of manipulating the adult sex ratio on pre- and post-mating reproductive traits. Chapter 2 uses proximate
manipulation of the adult sex ratio to show how the relationship between pre- and post-mating success is affected by the levels of male competition. Chapter 3 shows that selection lines are unable to select for the traits that predict male reproductive success under altered levels of male competition. Chapter 4 describes the attempts to produce RIDL genetic constructs with embryonic lethality. Chapter 5 demonstrates that RIDL lines of medfly display characteristics that make them suitable for wild population control and may exceed the performance of existing SIT lines. Chapter 6 shows that manipulation of the larval diet can alter the gut microbiota of adults; however these manipulations have no effect on reproductive behaviour. Instead there was a significant effect of high-sugar larval rearing on mating success and body mass. This effect persisted for a single generation in offspring of these flies, even when they were reared on an inferior starch-based larval diet. Finally Chapter 7 summarises the thesis and discusses the implications of this work and future directions for both research in the reproductive behaviour of the medfly, and the future of RIDL technology in medfly population control
