Effect of forced locomotion on the rest-activity cycle of the cockroach.

Many insects are known to exhibit clear circadian rest-activity rhythms. Attention has focussed more on active behaviors such as locomotion than on rest. I investigated the consequences of disturbances of the rest period on activity states of the cockroach Leucophea maderae. The 24-h rest-activity rhythm of individual animals maintained under a 12 h light-12 h dark schedule was continuously recorded by timelapse video recording. Three activity states were scored: locomotion, immobility, and limb or antenna movements without locomotion. The effect of (i) 3 h forced activity; and of (ii) handling and a new environment was studied. Forced activity during the last 3 h of the light period caused a significant reduction of locomotion, and of limb or antenna movements; and an enhancement of immobility in the first hours of the dark period. However, over the entire 12 h dark period, these parameters did not differ from control. Brief handling in conjunction with a change in environment during the last 3 h of the dark period, was followed by similar, though smaller changes in locomotion as seen after forced locomotion. The results indicate that the time spent in immobility corresponds to a resting state which is regulated as a function of prior activity. Thus immobility in an invertebrate may exhibit similar regulating mechanisms as rest or sleep in vertebrates.