Electromyography of Flight Muscles in Free-Flying Chestnut Tiger Butterfly, Parantica sita.

The chestnut tiger butterfly, Parantica sita, can undertake long-distance migrations. They flap their wings for power flight and hold the wings for gliding; such repertoires of wing movements may be the key to explaining their excellent flight abilities. Measuring flight muscle activity using the electromyogram (EMG) is the first step toward understanding the neuromuscular mechanism of active flight control. Free-flight EMG measurements have, however, not been reported in butterflies. This study developed a method to acquire two-channel EMGs from free-flying P. sita. Stable EMG recordings were acquired using a monopolar electrode by attaching a small pre-amplifier to the dorsal mesonotum. The common-mode noise between channels was resolved by inserting a reference electrode into the mesonotum midline. The EMGs of five flight muscles were measured during free-flight and their activation phases were analyzed. The EMGs of all five muscles demonstrated a burst of spikes per stroke cycle, in contrast to the few spikes per cycle in the EMGs of hawkmoths, which would reflect the differences in wing kinematics and flight abilities. Further analyses, combining the technique developed in this study with high-speed videography, will clarify the neuromuscular mechanisms underlying the flight ability of P. sita.