Whitefly have the highest contraction frequencies yet recorded in non-fibrillar flight muscles

Abstract

ASYNCHRONOUS (myogenic) insect flight muscles have evolved independently at least seven times¹. Although such muscles do not necessarily contract at particularly high frequencies, potentially they allow far greater wing stroke rates than synchronous muscle which, because of the delays involved in muscle activation, has been believed to be incapable of operating at frequencies above ∼ 100 Hz (ref. 2), unless power output is small and much of the muscle volume occupied by sarcoplasmic reticulum³. Asynchronous muscle has so far always been shown to be of the ‘fibrillar’ histological type, and this correspondence has been assumed to be invariable¹. Predictably, very small insects, for which a high stroke frequency is believed to be essential², almost always have fibrillar flight muscle. However, a few groups, notably the hemipterous family Aleyrodidae (whitefly), have muscle of the ‘close-packed’ type, hitherto supposed to operate only synchronously¹. We have measured cinematographically the wing-beat frequencies of the whitefly Trialeurodes vaporariorum (Westwood), and report here that they are well above the usually assumed limit for synchronous functioning. Either this limit, or the assumption that all asynchronous muscle is of fibrillar type, must therefore be incorrect.