Excitable spring-wing dynamics 1: Common dynamics and transitions between synchronous and asynchronous insect flight.

Centimeter scale biological fliers have adopted two seemingly distinct strategies for high-power, high-frequency flight. Some use time-periodic drive of resonant mechanical systems, termed synchronous flight. Others achieve self-excited, “asynchronous” oscillations via delayed stretch activation (dSA) in their flight muscles. dSA is a delayed rise in force following stretch that allows a pair of opposing dSA muscles to produce emergent limit cycle behavior. Here we unify the periodic drive and dSA activity of flight muscle under one framework. We first identify evolutionary transitions between the two strategies, suggesting that insects can transition from one regime to the other. We then show that synchronous moth muscle unexpectedly also has dSA, but at a scale insufficient to lead to emergent self-excitation. To address how discrete oscillatory behavior emerges from a continuum of actuator properties, we combined the two types of actuation with a resonant spring-wing mechanics model. In simulation, we show that the same dynamical system can produce both synchronous and asynchronous oscillations divided by an intermediate regime with no coherent oscillations. The traditional dichotomy of synchronous and asynchronous insect is therefore two regimes of a spring-wing dynamics.