Temperature and the ventilatory response to hypoxia in gromphadorhina portentosa (blattodea: Blaberidae)

Abstract: In general, insects respond to hypoxia by increasing ventilation frequency, as seen in most other animals. Higher body temperatures usually also increase ventilation rates, likely due to increases in metabolic rates. In ectothermic air-breathing vertebrates, body temperatures and hypoxia tend to interact significantly, with an increasing responsiveness of ventilation to hypoxia at higher temperatures. Here, we tested whether the same is true in insects, using the Madagascar hissing cockroach, Gromphadorhina portentosa (Schaum) (Blattodea: Blaberidae). We equilibrated individuals to a temperature (beginning at 20°C), and animals were exposed to step-wise decreases in P O2 (21, 15, 10, and 5 kPa, in that order), and we measured ventilation frequencies from videotapes of abdominal pumping after 15 min of exposure to the test oxygen level. We then raised the temperature by 5°C, and the protocol was repeated, with tests run at 20, 25, 30, and 35°C. The 20°C animals had high initial ventilation rates, possibly due to handling stress, so these animals were excluded from subsequent analyses. Across all temperatures, ventilation increased in hypoxia, but only significantly at 5 kPa P O2. Surprisingly, there was no significant interaction between temperature and oxygen, and no significant effect of temperature on ventilation frequency from 25 to 35°C. Plausibly, the rise in metabolic rates at higher temperatures in insects is made possible by increasing other aspects of gas exchange, such as decreasing internal P O2, or increases in tidal volume, spiracular opening (duration or amount), or removal of fluid from the tracheoles.