IN-VIVO MUSCLE LENGTH CHANGES IN BUMBLEBEES AND THE IN-VITRO EFFECTS ON WORK AND POWER

The amplitude and time course of muscle length changes were examined i n vivo in tethered, flying bumblebees Bombus lucorum. A 'window' was c ut in the dorsal cuticle and aluminium particles were placed on the ex posed dorsal longitudinal muscle fibres. Muscle oscillations were reco rded using high-speed video and a high-magnification lens. The amplitu de of muscle length changes was 1.9 % (S.D.=0.5 %, N=7), corresponding to the commonly quoted strain of 1-3 % for asynchronous muscle. Highe r harmonics, particularly the second, were found in the muscle oscilla tions and in the wing movements. The second harmonic for wing movement s was damped in comparison to that for muscle length changes, probably as a result of compliance in the thoracic linkage. Inclusion of the s econd harmonic in the driving signal for in vitro experiments on glyce rinated fibres generally resulted in a decrease in the work and power, but a substantial increase was found for some fibres.