Maximum metabolic rate, relative lift, wingbeat frequency, and stroke amplitude during tethered-flight in the adult locustLocusta migratoria

Abstract

SummaryFlying insects achieve the highest mass-specific aerobic metabolic rates of all animals. However, few studies attempt to maximise the metabolic cost of flight and so many estimates could be sub-maximal, especially where insects have been tethered. To address this issue, oxygen consumption was measured during tethered-flight in adult locusts Locusta migratoria, some of which had a weight attached to each wing (totalling 30-45% of body mass). Mass-specific metabolic rates (μmol O2 g-1 h-1) increase from 28 ± 2 at rest, to 896 ± 101 during flight in weighted locusts, and 1032 ± 69 in unweighted locusts. Maximum metabolic rate of locusts during tethered-flight (MMR; μmol O2 h-1) increases with body mass (Mb; g) according to the allometric equation, MMR = 994Mb0.75 ± 0.19, whereas published metabolic rates of moths and orchid bees during hovering free-flight (HMR) is approximately 2.8-fold higher, HMR = 2767Mb0.72 ± 0.08. The modest flight metabolic rate of locusts is unlikely to be an artefact of individuals failing to exert themselves, because mean maximum lift was not significantly different from body mass (95 ± 8%), mean wingbeat frequency was 23.7 ± 0.6 Hz, and mean stroke amplitude was 105 ± 5 degrees in the forewing and 96 ± 5 in the hindwing – all of which are close to free-flight values. Instead, the low cost of flight could reflect the relatively small size and relatively modest anatomical power-density of the locust flight motor, which is a likely evolutionary trade-off between flight muscle maintenance costs and aerial performance.