Technical Abstract: Southern green stink bugs, Nezara viridula (L.), and related species are significant pests of cotton in the U.S. Cotton Belt. Using their stylets, adults introduce disease pathogens of cotton into cotton bolls, and preliminary data indicates nymphs can also ingest these pathogens. Data is lacking regarding stylet penetration potential of N. viridula nymphs, however, and records of stylet penetration by adults are typically determined after damage has occurred. In this study, rostral segments of all developmental stages of N. viridula were measured to estimate potential stylet penetration using a novel mathematical model. Overall minimum and maximum observed lengths of rostrum ranged from 835.29 um (1st instars) to 7,088.16 um (adult females), and mean rostral lengths were significantly different between all stages. Overall mean stylet penetration estimates for all stages ranged from 135.33 um for 1st instars to 2,389.26 um for adult females. Potential stylet penetration significantly increased as the insect progressed through nymphal stages. Penetration was also significantly affected by insect posture while feeding. This report establishes conservative baselines of potential stylet penetration by all nymphal stages and adult sexes of N. viridula. Additionally, the model presented here can be used to estimate potential stylet penetration for other Hemiptera and closely related insects with similar modes of feeding. In conjunction with crop phenology data, accurate estimates of potential stylet penetration will allow more proactive approaches to pest management in a wide range of high-value cash crops affected worldwide by N. viridula.