The mating behavior and developmental reproductive biology of the soybean stem borer Dectes texanus texanus LeConte were studied. Adults live for up to a month, but reach sexual maturity and are able to mate at 5 d of age. At hour-long observation times between 0900 and 1700 hours, no peak time of mating was observed. Females did, however, stridulate more often between 0900 and 1300 hours. Males approach females and tap the surface of the female’s elytra and thorax with their antennae. Subsequently, the male mounts the female, strokes her elytra with his palpi, bends his abdomen, and copulates. Male responses to solvent washes of females suggest the use of a contact sex pheromone. Mature eggs are first observed in virgin female ovarioles at 14 d of age, whereas mated females (8 d old) are able to oviposit just 4–8 d after mating.