POWER OUTPUT FROM A FLIGHT-MUSCLE OF THE BUMBLEBEE BOMBUS-TERRESTRIS .1. SOME FEATURES OF THE DORSOVENTRAL FLIGHT-MUSCLE

1. Isometric contractions from the asynchronous dorso-ventral flight m uscle of the bumblebee Bombus terrestris were slow and rather weak. Th e twitch duration (onset to 50% relaxation) was approximately 300 ms a t 30 degrees C and 170 ms at 40 degrees C. The maximum tetanic tension was approximately 40 kN m(-2); the ratio of twitch force to tetanic f orce was approximately 0.2. 2. The unstimulated muscle was quite resis tant to stretch, with a low-frequency stiffness of 730 kN m(-2) at mus cle lengths close to that of the muscle in vivo. The length-tension cu rve for active tetanic tension (that is the increase in tension above the passive level during stimulation) was very narrow, with a half-wid th equal to only 17% of the optimal length. 3. The muscle strain durin g tethered flight was approximately 2% peak-to-peak, occasionally reac hing 3%. Strain amplitude increased with wing stroke frequency. The th oracic vibration frequency of escape buzzing, during which the wings a re not extended but are folded over the abdomen, was approximately twi ce that of tethered flight but the muscle strain was similar to that o f flight.