WING-BEAT COUPLING BETWEEN FLYING LOCUST PAIRS - PREFERRED PHASE AND LIFT ENHANCEMENT

Pairs of locusts flying in tandem in a wind tunnel are known to couple their wing-beats intermittently. The rhythmically oscillating air how from the front locust's wing-beat, detected by the rear individual, a ppears to convey the timing information for coupling, Three prediction s of this arrangement were tested quantitatively in this study. (1) Gi ven that the oscillating air how has a wavelength of 7.5 cm, placing t he rear locust 7.5 or 15 cm behind the front one should produce the sa me phase of coupling, whereas placing it at an intermediate distance o f 11 cm should produce an opposite phase. (2) At any distance, the pre ferred phase at which wing-beat coupling occurs should depend, in part , on the difference in the wing-beat frequencies of the two locusts ju st before the coupling began. (3) At the moment that the wing-beats of the two locusts become coupled, a change should be observed consisten tly in the wing-beat frequency of the rear individual only. Each of th ese three predictions was fulfilled. We also recorded the instantaneou s lift of the rear locust by tethering it to a laser torque meter. Lif t varied with the phase of the wing-beats between the two locusts. For a given distance between the two locusts, lift was greater by a mean of 16% of the locust's body mass at those phases where coupling most c ommonly occurred than at opposite phases. This lift effect was seen ev en if the wing-beats of the two locusts drifted through these preferre d phases without actually coupling. These results are discussed in ter ms of a possible energetic advantage conferred to the rear locust by f lying in tandem and by coupling its flight rhythm to the leader's wing -beat.