Abstract: The antibacterial response of tobacco budworm (Heliothis virescens) larvae vaccinated with the bacterium Enterobacter cloacae peaked at 6-30 h following vaccination was significantly higher than the antibacterial response of unvaccinated larvae. The effect of immune hemolymph from H. virescens larvae was determined by the growth of Escherichia coli (strain K12 D31) on tryptic soy agar mixed with the immune hemolymph. The range of increase in bactericidal activity seen during this time period was from 49.1 to 71.1%. The greatest bactericidal activity (up to 71.1%) was observed from 12-20 h following the initial infection. A second vaccination (reinfection) with E. cloacae at 48 h following the initial vaccination did not result in any long-term potentiation of the larval antibacterial response, although it did boost short-term bactericidal activity by 3.1% after 12 h. This indicates that an anamnestic (memory) response is likely not elicited. The data demonstrated the time sequence in the antibacterial response of H. virescens larvae.