Locust Wind Receptors

ABSTRACT Tethered locusts begin opening their wings about 45 msec, following wind stimulation of the facial setae. Tethered locusts also begin wing opening at least 30 msec, after release of tarsal contact with the substratum. High-speed ciné photography reveals that an untethered locust in a take-off jump initiates wing opening as early as 15 msec, after the first detectable jumping motion. Therefore in free jumps neither stimulation of the facial setae by the jump wind nor release of tarsal contact is the factor inducing wing opening. The actual mechanism acts much more rapidly, and probably involves central, rather than peripheral, coding. During flight, the extent of forewing pronation on the downstroke is a function of the wind speed over the facial setae, higher speeds resulting in decreased pronation. With increasing wind speed no change in pronation appears until about 80 msec., after which the effect is exaggerated for several hundred milliseconds, finally trailing off slightly to the maintained level. The data suggest that the ‘wind-indicator’ interneurones of the cervical connective are active in the lift-control reflex. A suggested behavioural function of this reflex is rapid ascent following the acceleration produced by a take-off jump.