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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]

Measuring metabolic rate (MR) poses a formidable challenge in free-flying insects who cannot breathe into masks or be trained to fly in controlled settings. Consequently, flight MR has been predominantly measured on hovering or tethered insects flying in closed systems. Stable isotopes such as labelled water allow measurement of MR in free-flying animals but integrates the measurement over long periods exceeding the average flight duration of insects. Here, we applied the 'bolus injection of isotopic 13C Na-bicarbonate' method to insects to measure their flight MR and report a 90% accuracy compared to respirometry. We applied the method on two beetle species, measuring MR during free flight and tethered flight in a wind tunnel. We also demonstrate the ability to repeatedly use the technique on the same individual. Therefore, the method provides a simple, reliable and accurate tool that solves a long-lasting limitation on insect flight research by enabling the measurement of MR during free flight. [ABSTRACT FROM AUTHOR]

Measuring metabolic rate (MR) poses a formidable challenge in free-flying insects who cannot breathe into masks or be trained to fly in controlled settings. Consequently, flight MR has been predominantly measured on hovering or tethered insects flying in closed systems. Stable isotopes such as labelled water allow measurement of MR in free-flying animals but integrates the measurement over long periods exceeding the average flight duration of insects. Here, we applied the 'bolus injection of isotopic 13 C Na-bicarbonate' method to insects to measure their flight MR and report a 90% accuracy compared to respirometry. We applied the method on two beetle species, measuring MR during free flight and tethered flight in a wind tunnel. We also demonstrate the ability to repeatedly use the technique on the same individual. Therefore, the method provides a simple, reliable and accurate tool that solves a long-lasting limitation on insect flight research by enabling the measurement of MR during free flight.

The distance a small insect moves through the air during a jump is limited by the launch velocity at take-off and by air resistance. The launch velocity is limited by the length of the jumping legs and the maximum power that the jump apparatus can provide for pushing against the ground. The effect of air resistance is determined by the insect mass-to-area ratio. Both limitations are highly dependent on body size, making high jumps a challenge for smaller insects. We studied both effects in the tiny Encyrtid wasp Anagyrus pseudococci. Males are smaller than females (mean body length 1.2 and 1.8 mm, respectively), but both sexes take off in a powerful jump. Using high-speed cameras, we analyzed the relationship between take-off kinematics and distance traveled through the air. We show that the velocity, acceleration and mass-specific power when leaving the ground places A. pseudococci among the most prominent jumpers of the insect world. However, the absolute distance moved through the air is modest compared with other jumping insects, as a result of air resistance acting on the small body. A biomechanical model suggests that air resistance reduces the jump distance of these insects by 49% compared with jumping in the absence of air resistance. The effect of air resistance is more pronounced in the smaller males, resulting in a segregation of the jumping performance between sexes. The limiting effect of air resistance is inversely proportional to body mass, seriously constraining jumping as a form of moving through the air in these and other small insects., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)