Hemiptera success can be partially attributed to their scent glands, which are dorsal abdominal glands (DAGs) in nymphs. Recent studies on Pentatomoidea have described cuticular modifications associated with DAGs, which compose the scent efferent system (SES), but the ontogeny has been poorly documented. We aim to—1) search for new SES characters in two representative species of Pentatomidae; 2) describe the SES ontogeny after hatching; and 3) compare the SES morphology between two species. Adults and immature samples from the first to fifth instars of Chinavia obstinata (Stål) (Pentatominae) and Cyrtocoris egeris Packauskas & Schaefer (Cyrtocorinae) were used as pentatomid representatives. SES structures were evaluated using scanning electron microscopy. Features that were never evaluated before are described: the scent efferent system orientation, periostiolar flap, periostiolar area, postostiolar projection, and peritreme lip. We observed remarkable differences between the first and second instars in both species, especially for DAGs 2 and 3; from the second to fifth instar, the modifications were subtle. Only the DAG1 scent efferent system persists in adults. The characteristics that present broader morphological diversity in the Pentatomomorpha are the following: peritreme, evaporatorium microsculpture, scent efferent system orientation, and peritreme lip. We conclude that any sample between the second and fifth instars can be used for species description and character extraction. We recommend using both traditional structures and the newly evaluated features in future descriptive and comparative studies for Pentatomomorpha.