SHORT COMMUNICATION FLIGHT BEHAVIOUR AND SELECTIVE DEGENERATION OF FLIGHT MUSCLES IN THE ADULT CRICKET (GRYLLUS BIMACULATUS)

Tethered adult crickets (Gryllus bimaculatus De Geer) assume a full flight posture: they point the antennae straight ahead, hold the fore- and midlegs close to the body, stiffen the abdomen for steering and extend the hindlegs directly backwards. Tomioka and Yamaguchi (1980) have reported that about 30 % of the animals displaying flight behaviour also flap their hindwings, but the remaining crickets vibrate their wings through a narrow range instead of flapping them. They distinguished the latter type of behaviour from normal flight behaviour and designated it 'pseudo-flight behaviour'. Degeneration of flight muscles is known to occur in young adult insects of several orders (Finlayson, 1975; Collatz and Wilps, 1986). It has been reported that in the cricket Teleogryllus oceanicus the dorsal longitudinal muscle atrophies and becomes white in appearance in late adult life (Ready and Josephson, 1982; Ready and Najm, 1985) and in the cricket Acheta domestica the dorsal longitudinal muscle increases in size during the first 2 days after the imaginal moult, but begins to degenerate on the fourth day in the presence of juvenile hormones (Chudakova and Bocharova-Messner, 1968; Srihari et al. 1975). The present experiments were designed to detect any close relationship between flight behaviour and age-related degeneration of flight muscles during adult life. Crickets (Gryllus bimaculatus) were reared at 28°C under a 12h:12h L:D photoperiod. Maximal adult life span was about 20 days under these conditions. The flight behaviour of each individual was tested daily after the imaginal moult, as follows. The flight behaviour of the tethered cricket, held stationary in spac