The Effect of Ambient Humidity on the Metabolic Rate and Respiratory Patterns of the Hissing Cockroach, Gromphadorhina portentosa (Blattodea: Blaberidae)

Abstract

We examined the effects of humidity on the metabolic rates and respiratory patterns of Gromphadorhina portentosa (Schaum) (Blattodea: Blaberidae) to determine whether insects transition from continuous, cyclical, and discontinuous (DGC) respiration in response to water conservation. Eight male G. portentosa were placed under five different humidity treatments (0, 23, 40, 60, 80% RH). Using flow through respirometry we: (i) determined the effect of humidity on metabolic rate; (ii) observed if changes in metabolic rate were correlated with changes in closed/flutter (CF) or the open (O) phase of DGC; and (iii) determined whether increased spiracular closure was correlated with an increase in water retention. Although G. portentosa had similar rates of CO2 release when placed under 0, 40, 60, and 80% RH, cockroaches placed at 23% RH had a significantly higher metabolic rate. There was no effect of humidity on the duration of the CF phase of the DGC. However, the O phase of DGC was significantly longer when G. portentosa was placed at humidity levels above 23% RH. Interestingly, we saw that the average rate of mass lost to the environment did not change when cockroaches were placed at humidity levels ranging from 0 to 80% RH. This suggests that modulation of the spiracles allows G. portentosa to regulate the amount of water lost to the environment.

Water Costs of Gas Exchange by a Speckled Cockroach and a Darkling Beetle

“…CGE and cyclic are the ancestral patterns, as all spiracles do not seal completely or simultaneously during gas exchange. In CGE, the spiracles remain open and the gas exchange is regular, often to support maximum gas exchange in active species [8][9][10]. Cyclic gas exchange consists of alternating burst and interburst phases that produce periodic gas exchange, but the spiracles never close completely and simultaneously [11].…”

Intraspecific variation in metabolic rate and its correlation with local environment in the Chinese scorpionMesobuthus martensii

“…For instance, a positive influence of precipitation on RMR was observed across snake species (Dupoué et al, 2017). Recently, Vrtar et al (2018) showed that experimentally controlled humidity can significantly affect the RMR of the hissing cockroach. Unfortunately, in ectotherms, few studies have focused on the relationship between local humidity and RMR among populations.…”