動物学：高速で飛翔する小型甲虫の秘密

The distinctive flight style and light, bristled wings of one of the smallest insects in the world, the featherwing beetle, could explain its superb flight performance, according to a paper published in Nature. These findings are important for increasing our understanding of the evolution of flight at the miniature scale.

How fast an insect flies is generally dictated by its size: the larger the insect, the faster the flight. This discrepancy is usually down to constraints in terms of air friction, which usually outweighs flight power at very small scales. However, some miniature insects appear to contradict this rule. One example is the featherwing beetle (Paratuposa placentis), which is less than half a millimetre in size (395 μm) but can fly at speeds similar to those achieved by insects that are three times bigger.

Alexey Polilov and colleagues combine 3D reconstructions of the structure and motion of the wings of P. placentis. The team reveal that this beetle not only has bristled wings that are lighter than membranous wings of equivalent size, but also that these wings move in a previously unknown way. The beetle has a wing-beating cycle of two power half strokes that produce a large upward force, followed by two slow recovery strokes that produce a smaller, downward force. This cycle increases the amplitude of the wing strokes. The elytra (hardened forewings) function as brakes to stop excessive oscillations. Bristled wings also may not require as much muscle power as that needed for heavier membranous wings, the authors suggest, therefore counteracting any potential increases in demand resulting from this unique movement cycle.

The authors conclude that these adaptations could explain how such an excellent flight performance has been preserved by tiny insects during the process of miniaturization, representing what could be an important component of their evolutionary success.