‘Paradoxical Driving’ of Walking Activity in Locusts

Abstract

ABSTRACT Gregarious fifth-instar larvae of Locusta migratoria migratorioides were placed singly on a counterbalanced, recording treadmill providing precise measurements of (i) walking bout length, (ii) non-walking bout length, (iii) walking speed and (iv) distance walked, over periods of hours. Under constant conditions in light the walking activity was often inter-rupted but gradually built up to a high intensity which was then sustained for 1−2 h before finally declining; there were orderly relations between the measured behavioural components. In continuous darkness walking activity was less interrupted but less intense and quickly declined; there were less orderly relations between the components. Under alternating 10 min periods of light and darkness the relations between the behavioural components were again more orderly in the light than the dark. However, walking activity was sharply depressed in these short light periods but was promptly resumed in each subsequent dark period and grew stronger as the fight–dark alternation continued. These diverse and at first sight paradoxical results are all consistent with the principle of post-inhibitory rebound (‘antagonistic induction’). This type of behavioural after-effect, acting on different time scales, is exemplified by the surge of walking observed in the dark on the release of the experimentally applied inhibition of walking by light, as well as by the build-up and sustained walking in continuous light (‘paradoxical driving’).