The effects of the bacterium Serratia marcescens (Bizio) was investigated on the F₁ generation of laboratory-reared Heliothis virescens (F.). There was no difference in adult male or female longevity (i.e., parental generation) for individuals inoculated with S. marcescens as larvae (Serratia treatment) and those that were free of the bacterium (control treatment). However, the number of eggs laid and the prevalence of eclosion of eggs from Serratia treatment adults were reduced relative to control treatment adults. A very low number of F₁ Serratia treatment eggs exhibited signs of infection, but a higher prevalence of mortality was observed for F₁ larvae (n = 2,888) for the Serratia (3.5–4.6%) than for the control (1.1–1.5%) treatment. No S. marcescens was isolated from dead control larvae; whereas, 48–54% of dead F₁ larvae for the Serratia treatment were positive for the bacterium. However, there was no significant difference in larval weights between treatments. There were also no differences in either mortality or weight of F₁ male pupae between treatments, but F₁ female pupae were significantly smaller and prevalence of mortality was higher for the Serratia treatment. Serratia marcescens was not isolated from any of the control F₁ pupae, but 6% of pupal cadavers for the Serratia treatment were positive for the bacterium. No S. marcescens was recovered from the meconia of any of the F₁ adults (n = 2,600) regardless of treatment, and there were no differences in adult weights between treatments. Although sublethal effects of S. marcescens were detected, the impact and prevalence of the bacterium were tremendously reduced over the F₁ generation in the absence of all but the most basic management strategies.