The role of the mesothoracic spiracles in respiration in flighted and flightless dung beetles

The relative role of the mesothoracic and abdominal spiracles in respiration was examined using flow-through respirometry in four dung beetle species from different habitats. Two species of flightless beetles, Scarabaeus (Pachysoma) gariepinus and Scarabaeus (Pachysoma) striatum, from the arid western region of southern Africa and a large flighted species, Pachylomerus femoralis, from a more mesic habitat were compared with Circellium bacchus, a flightless beetle from a low rainfall eastern area. All species showed a form of the discontinuous gas exchange pattern at rest. The mesic flighted species used a closed, flutter, open, cycle (CFO) while those species from more arid habitats used a closed, ventilation, cycle (CV) or a closed, burst cycle (CB). The relative importance of the mesothoracic spiracles in CO2 emission varied between the species, even between those from the same genus and habitat. C. bacchus and P. femoralis represent extremes of CO2 emission from the mesothoracic spiracles; from almost total to almost none, respectively. Overall, mesothoracic CO2 emission and convection were more pronounced in the dry habitat species, supporting the hypothesis that both strategies aid in the reduction of water loss.