The properties of asynchronous insect flight muscle have been examined using a glycerol- extracted single-fibre preparation of dorsal longitudinal muscle from the bumblebees Bombus lucorum and B. terrestris. Chemical, mechanical and thermal conditions were controlled with the objective of maximizing power output. The problems arising from diffusion limitation were avoided through a combination of fibre paring and the use of an ATP backup system. Work and power output tended to increase with increasing oscillatory strain in the range 1–5 %. Workloop shape, and hence work and power, varied with fibre extension; optimum extensions ranged from 4 to 12 %. The mechanical performance of glycerinated bumblebee muscle fibres was strongly temperature-dependent, and rate processes (frequency, power) displayed higher thermal sensitivities than processes associated with tension development (work). The experimental conditions that maximized the power output were identified as: oscillatory strain epsilon=4-5 %, extension epsilono=8-10 %, oscillation frequency f=50 Hz and temperature T=40°C. The maximum power output observed under these ‘optimal’ conditions was about 110 W kg-1 (muscle), demonstrating for the first time that glycerinated fibres are capable of producing the power predicted from free-flight studies to be required for flight: 100 W kg-1.

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