Search

The scaling of the energetic cost of locomotion with body mass is well documented at the interspecific level. However, methodological restrictions limit our understanding of the scaling of flight metabolic rate (MR) in free‐flying insects. This is particularly true at the intraspecific level, where variation in body mass and flight energetics may have direct consequences for the fitness of an individual. We applied a 13C stable isotope method to investigate the scaling of MR with body mass during free‐flight in the beetle Batocera rufomaculata. This species exhibits large intraspecific variation in adult body mass as a consequence of the environmental conditions during larval growth. We show that the flight‐MR scales with body mass to the power of 0.57, with smaller conspecifics possessing up to 2.3 fold higher mass‐specific flight MR than larger ones. Whereas the scaling exponent of free‐flight MR was found to be like that determined for tethered‐flight, the energy expenditure during free‐flight was more than 2.7 fold higher than for tethered‐flight. The metabolic cost of flight should therefore be studied under free‐flight conditions, a requirement now enabled by the 13C technique described herein for insect flight. [ABSTRACT FROM AUTHOR]

Insects exchange respiratory gases with their environment through their gas-filled tracheal system, a branched tracheal tree extending from segmental openings and terminating at fine tissue penetrating tracheoles. It was shown that the tracheal volume increases hyperallometrically with insect body size (M b), both interspecifically and across developmental stages. In this study, we used the sixfold M b variation in adult Batocera rufomaculata (Cerambicidae; Coleoptera) examining the allometry of adult tracheal volume (V tr ). We further explored the effect of sex and sexual maturity on tracheal gas conductance, testing the hypotheses that (i) larger body size and (ii) egg volume in gravid females would result in lower safety margins for tracheal oxygen transport due to structural restriction. We report a hyperallometric tracheal growth in both sexes of adult B. rufomaculata (mean mass exponent of 1.42 ± 0.09), similar in magnitude to previously reported values. Tracheal gas conductance was independent of M b and reproductive state, but was significantly higher in females compared with males. We suggest that females may have pre-adapted a higher tracheal conductance required for the higher flight power output while gravid. Lack of compliant air sacs and rigid trachea may explain how gravid females retain their V tr . However, we show that V tr outgrows thoracic dimensions with increased B. rufomaculata size. Hyperallometric growth of the giant cerambycid thoracic trachea could explain the previously reported hypometric scaling of flight muscles in B. rufomaculata , and the compromised long-distance flight performance of larger compared with smaller conspecifics. [ABSTRACT FROM AUTHOR]