All insects have a segmented body. The genes controlling segment development have been well characterized in the fruit fly, Drosophila melanogaster. These genes were divided into three categories: gap genes specify several continuous segments over a broad region of the embryo; Pair-Rule Genes (PRG) are responsible for segment formation and are the first set of genes to be expressed in repetitive patterns in the embryo; Segment polarity genes define anterior and posterior polarities within each segment.To understand how PRGs evolve, I took a comparative approach in this thesis. First, I compared the function of the Drosophila PRG ftz-f1 to that of its mammalian orthologs by expressing them all in Drosophila embryos. I found that the molecular function of this family of nuclear receptors has been highly conserved during evolution.

Next, I set out to establish new insect model systems to study PRG function.  While, some PRGs have been studied in other insects, most of these studies focused on holometabolous insects. My work focused on the sister group to the holometabolous insects, the Hemipteroid Assemblage. I participated in the genome annotation of a hemipteras insect, Oncopeltus fasciatus. I annotated nuclear receptor super family, Hox and PRGs in Oncopeltus.  I further studied the expression and function of four PRGs in Oncopeltus. Using in situ hybridization and RNAi, I found that, Of-ftz and Of-hairy do not have segmentation function, while Of-ftz-f1 has function in oogenesis and segmentation. Of-runt was found to induce cell death in oocytes, but its function in segmentation needs further analysis.  Using the knowledge and expertise I gained from Oncopeltus, I successfully set up in situ hybridization, antibody staining and parental RNAi in an invasive hemipteran insect pest, the Brown Marmorated Stink Bug (BMSB) Halyomorpha halys.  These studies show that the expression and function of PRGs varies extensively in diverse insects, despite the overall conservation of a segmented body plan.