Variability of motor output during flight steering in locusts

Abstract

1. A flight balance has been used to demonstrate the generation of torques by a flying locust,Locusta migratoria, in response to roll movements of an artificial horizon. 2. The movements of the horizon can be perceived by either the compound eyes or the ocelli alone and lead to roll responses from the animal. 3. Amputation experiments show that either fore- or hindwings alone are able to produce a roll response of appropriate sign. 4. EMGs have been recorded from the flight muscles. Shifts in the relative latency between homologous pairs of depressor and elevator muscles are frequently correlated with roll responses. The directions of these shifts are opposite in the fore- and hindwings. The relative latencies of both elevators and depressors of a given wing shift in parallel. 5. No systematic changes in burst length correlated with roll responses are seen. This may be a consequence of the experimental conditions. 6. Roll torques can be developed without changes in the relative firing times of basalar (pronator) and subalar (supinator) muscles. 7. Changes in wingbeat amplitude are not always systematically correlated with roll responses. 8. Both fore- and hindwings beat out of phase during roll responses, a wing being advanced or retarded in its cycle in comparison to its contralateral homologue. As seen for latency shifts, the direction of these phase shifts is reversed between fore- and hindwings. The phase shift of the wing is probably the main result of the latency shifts of the flight muscles. 9. The motor output alterations which occur during roll responses of flying locusts are variable. The magnitude of the latency shifts can vary, changes in burst length are not indispensable, and neither rudderlike movements of the abdomen and the hindlegs nor changes in the wingbeat amplitude are necessarily correlated with torques. The flying locust is in every case producing a roll response.