Recent studies to elucidate relationships between the western tarnished plant bug, Lygus hesperus Knight, and injury to cotton (Gossypium spp.) have identified important differences in feeding behaviors among adults of different gender and reproductive states. These findings suggest a need for improved knowledge of L. hesperus temperature-dependent reproductive development. We used nonlinear biophysical development rate models to describe the reproductive development of adult L. hesperus held under constant temperatures from 12.8 to 35.0°C. In addition, abdominal coloration was measured as a nondestructive indicator of reproductive maturity. The nonlinear models indicated most stages of ovary, seminal vesicle, and medial accessory gland development were subject to mild high-temperature inhibition, except for the stage of filled seminal vesicles. Development of filled seminal vesicles was subject to minor low-temperature inhibition and severe high-temperature inhibition. Estimated development times reflected extensive interindividual variation, especially at low temperatures. This variation suggests the opportunity to select for more rapid or more consistent reproductive development under the conditions of laboratory culture. Although presence of a dark aqua coloration of the ventral abdominal cuticle was statistically associated with reproductive maturity, especially in female L. hesperus, color-based predictions of reproductive maturity were often inaccurate for bugs reared at temperatures above or below 26.7°C. Therefore, use of abdominal coloration as an indicator of reproductive development in ecological studies seems inappropriate. The results provide mathematical descriptions of L. hesperus temperature-dependent reproductive development which should facilitate improved planning and interpretation of studies involving manipulation of adult reproductive status.