Energetics of Cockroach Locomotion

Abstract

Cockroaches, Gromphadorhina portentosa, were run at different speeds for 20 min on a miniature treadmill enclosed in a lucite respirometer while oxygen consumption (V_O2) was continuously monitored. The data collected on these 5 g insects are remarkably similar to those obtained on vertebrates. V_O2 rises rapidly with the onset of exercise; the t_½ on-response was about 1 min with steady-state reached within 4 min at the fastest speed, 0.12 km/h. Recovery was rapid; the t_½ off-response was 4–6 min, with total recovery achieved in less than 1 h. The tracheal system appears to be a highly efficient mode of O₂ conductance in contrast to the crustacean method of delivery involving gills and circulation. V_O2 (ml O₂/g.h) at steady-state running varies directly with velocity (V). The regression equation at 24 °C is V_O2 = 0.45+4.92V. The Y-intercept, at zero velocity, is 2.4 times the actual resting V_O2 rate of 0.19 ml O₂/g.h. Temperature does not change the slope of the regression line but shifts it up or down in accordance with a simple Q₁₀ effect. Incline running produces no changes compared to level running. The minimum cost of transport, the lowest V_O2 necessary to transport a given mass a specific distance, is high in cockroaches (4.92 ml O₂/g.km) and comparable to that expected for a small quadrupedal or bipedal pedestrian vertebrate.