Moth resonant mechanics are tuned to wingbeat frequency and energetic demands.

Flying insects have an elastic thorax, resulting in a dilemma faced by all resonant systems: match their wingbeat frequency to resonance to increase efficiency or flap off of their resonant peak to rapidly control wingbeat frequency. But how do diverse insects with different wingbeat frequencies and performance demands balance efficiency and agility through their resonant properties? We used materials testing, high-speed videography, and a model of resonant aerodynamics to show that the resonant frequency of hawkmoths and silkmoths scales with wingbeat frequency, but not because of changes stiffness of the thoracic exoskeleton. Instead, wing transmission ratio and wing inertia both change in a correlated way across species. Moreover, there is an offset in the wingbeat frequency to resonant frequency relationship such that most moths are supra-resonant, thereby balancing control and efficiency. However, there are also different resonant efficiencies that reflect clade-specific energetic demands because most wild silkmoths do not feed as adults, while hawkmoths are agile foragers. ### Competing Interest Statement The authors have declared no competing interest.