Activity of the direct downstroke flight muscles ofLocusta migratoria (L.) during steering behaviour in flight

Summary

The locust,Locusta migratoria (L.), performs tethered flight in the laminar flow of a wind tunnel. The animal is fixed ventrally to a stimulus device which produces rotations (max. rotation angle ± 15°) (Fig. 2). Depending upon the position of the axes relative to space and to the animal the latter is forced to rotate in the frontal, mediosagittal, or transversal plane. Simultaneous electromyograms from the direct downstroke muscles of the wings (7 electrodes implanted on each side in the following muscles, numbered after Snodgras: forewing 97, 98, 99, hindwing 127, 128, 129, in the last 2 electrodes) are made and analysed by means of a special data acquisition processor (Fig. 1) and digital computer.

One observes shifts in the time of occurrence (‘time shifts’) of the action potentials of muscles belonging to the same wing and to different wings. For example: A 20° rotation is correlated with a time shift of up to 6 ms between the muscles 97₁ and 99₁ (left forewing) and between 99₁ and 127₁ (different wings) (Fig. 8b).

On rotating the animal to the left within the frontal plane (yaw) (Figs. 7, 8), the left side muscles 97₁, 98₁, 127₁, and 128₁ fire earlier and the muscles 99₁ and 129_{1+2, 1} fire later than during straight ahead flight whilst on the right side the muscles 97_r, 98_r, 127_r, and 128_r fire later and 99_r and 129_{1+2, r} fire earlier.

On rotation within the mediosagittal plane (pitch) (Fig. 9), the muscles 97, 98, and 129₁₊₂ on both sides fire earlier when the head is raised, whereas 99 fires later. No definite statement can be made about the behaviour of the remaining downstroke muscles.

On rotation towards the right within the transversal plane (roll) (Fig. 10), the downstroke muscles of the left forewing fire earlier whereas those on the right fire later. No general scheme can be derived for both hindwing downstroke muscles.

Thus the behaviour of the direct downstroke muscles is essentially symmetrical to the position of the axes of rotation as far as the time shifts are concerned (Fig. 11).

In general (despite certain exceptions, see Fig. 12), the time shift curves vary so greatly that no definite coupling between different muscles should be assumed.