Slow-acting flight muscles of saturniid moths

Large saturniid moths (Philosamia cynthia and Saturnia piri) examined in this study are characterized by very slow flight (five to six wing beats/sec). Flight muscle fibers examined are in some ways typical for other types of insect synchronous flight muscles. However, two distinct differences were noted. First, they have a 6–7:1 thin-to-thick myofilament ratio. Second, they have unusually large T-tubule cavities containing an electron-opaque, floeculent material. The myofilament ratio is similar to that typical for slow, tonic-type rather than fast, phasic-type insect muscle fibers. It is suggested that the electron-opaque material found within these rather large T-tubule cavities and their large size may reflect another as yet unknown function, as well as that of excitation contraction coupling.