Female insects typically produce prodigious numbers of eggs to assure the propagation of their genes, and invest considerable resources towards this end. Ulti- mately, the egg of an insect must contain a haploid set of chromosomes, sufficient nutrients to supply the growing embryo with resources to last until the larva or nymph ecloses and begins feeding, and a set of determinants to direct the organization and progres- sion of embryogenesis, including the differentiation of a new cluster of germ cells. As with all organs, the morphology of the ovary reflects the physical and genetic requirements of its physiological role, which in this case is the functional assembly of the various components of the oocyte.

Visual inspection shows that the polytrophic ovary of holometabolus insects, which represent a major focus of this chapter, is comprised of a series of ovarioles that contain linear arrays of progres- sively developing follicles starting with dividing germ stem cells at one end and ending with mature oocytes ready for fertilization at the other ( Figure 1). Essentially, the ovariole can be considered an assem- bly line leading to the production of the egg. How this assembly line operates within different species to produce similar end products, i.e., the mature oocytes, depends on the insect, its life style, and its evolutionary history.