Female reproductive molecules—Still much to learn

Reproduction in sexual organisms is a complex process that involves various mechanisms and sex-specific molecules that through interacting steps ultimately result in fertilization between two gametes. Female insects have evolved various methods to assure successful reproduction. While previous work led to the identification and description of male ejaculatory components such as sperm and seminal fluid proteins and advanced our understanding of their function over the last decades, we still lack a comparable deep understanding of female reproductive molecules and their function. This chapter therefore focusses on female reproduction and reviews our current knowledge of female reproductive molecules and the regulation of key processes ensuring successful reproduction. We first review the general characteristics of the reproductive tract for female insects with a focus on mating-induced morphological and physiological changes of the reproductive tract, the female contributions to sperm storage and maintenance and the processes involved in successful fertilization. Then, we focus on molecules and pathways involved in the regulation of egg maturation and give a general overview on egg production including vitellogenesis and oogenesis. While some processes like oogenesis are well resolved, we will outline that other important ones are less well known and there is still much knowledge to be gained from studying the diverse aspects of female reproduction. While we mostly draw from insights gained on the model system Drosophila melanogaster, this chapter also draws on insights gained in other insect species. Thus we aimed to give a broad overview of our understanding of insect female reproduction with a particular focus on the reproductive molecules underpinning the complex process from mating over sperm storage and egg production to fertilization.