Respiration and Ventilation Responses to Acute Hypoxic Stress in the Guyana Orange Spotted Cockroach

Abstract

Insect ventilation follows characteristic patterns, from the discontinuous gas exchange cycle (DGC), with periods of open and closed spiracles (bursts and interbursts), to continuous gas exchange. Resting insects are relatively resistant to changes in ambient pO2 with respiration rates maintained by changes in ventilation pattern during hypoxic exposure. We measured CO2 release (Vco2) of the Guyana Orange Spotted Cockroach (Blaptica dubia) to test the hypothesis that B. dubia increases ventilation and transitions from DGC to continuous gas exchange in response to acute decreases in pO2 from 21kPa O2 to 3 kPa O2 at 25°C and 35°C. Between 21 and 6 kPa O2, animals had a significantly higher Vco2 at 35°C than at 25°C. Cockroaches increased total Vco2 at the lowest O2 level at 25°C, but not at 35°C. Mean burst and interburst Vco2 during severe hypoxia (3kPa pO2) at 35°C was higher when compared to values at 21kPa O2. Mean cycle rate during a burst increased as pO2 decreased at both temperatures. Interburst period increased significantly under severe hypoxia at 35°C. Overall, animals at the higher temperature had higher Vco2, and as O2 decreased the spiracles opened more during interbursts; hyperventilation begins during moderate hypoxia (6 kPa O2), but bursts become less frequent and ventilation becomes more continuous in severe hypoxia. Supported by NSF IOS 1146758 (EMD).