Holometabolous insects, which have distinct larval and pupal stages, evolved among hemimetabolous insects, which have nymphal stages. Currently, there are two main theories to explain how metamorphosis evolved, but the issue remains unresolved. To address this issue, we have been investigating the roles of histone modifiers in a holometabolous insect, the red flour beetle Tribolium castaneum, and a hemimetabolous insect, the milkweed bug Oncopeltus fasciatus. In T. castaneum, knock down of the epigenetic regulators Polycomb (Pc) and Enhancer of zeste (E(z)) during the pupal stage led to drastic homeotic transformations in the adults. This demonstrates that Pc and E(z) play key roles in determining segmental identity during metamorphosis. We are currently researching the roles of Pc and E(z) in the development of Oncopeltus fasciatus, a species of hemimetabolous insects. We will present data comparing the timing of action of Pc and E(z) through the use of RNA interference and through the use of quantitative PCR. The results from this study may help clarify the evolution of insect metamorphosis.