Respiration rates and drowning times after complete submergence were observed in diapausing Heliothis zea (Boddie) pupae at 5, 10, 15, 20, and 27°C. Respiration rate in pupae 2.5–12 weeks in diapause increased as an exponential function of temperature. The respiration rate of post-diapause pupae at 27°C increased over 10-fold in an approximately linear fashion during 12 days of pharate adult development. Time to 50% drowning in diapausing pupae decreased with increasing temperature, varying from 22.9 to 4.1 days at 5 and 27°C, respectively. Drowning rates in these pupae increased approximately exponentially with temperature. Diapausing and post-diapause pupae at 27°C had similar times to 50% drowning. An empirical model of drowning fitted the results well at all five temperatures, but a mechanistic model based on respiration predicted drowning considerably before it was observed. When the latter model was modified to allow withdrawal of dissolved oxygen from the water, it predicted longer survival periods, as observed. Our evidence suggests that respiration and drowning rates are closely correlated. Given the long survival times under complete submergence at 5–20°C, we speculate that pupae overwintering in the field in deep diapause are relatively resistant to drowning, whereas pre- and post-diapause pupae, with higher respiration rates, are at much greater risk.