Mangrove forests are influenced by tidal flooding and ebbing for a period of approximately 12.4 hours (tidal cycle). Mangrove crickets ( Apteronemobius asahinai ) forage on mangrove forest floors only during low tide. Under constant darkness, most crickets showed a clear bimodal daily pattern in their locomotor activity for at least 24 days; the active phases of approximately 10 hours alternated with inactive phases of approximately 2 hours, which coincided with the time of high tide in the field. The free-running period was 12.56±0.13 hours (mean±s.d., n =11). This endogenous rhythm was not entrained by the subsequent 24 hours light–dark cycle, although it was suppressed in the photophase; the active phase in the scotophase continued from the active phase in the previous constant darkness, with no phase shift. The endogenous rhythm was assumed to be a circatidal rhythm. On the other hand, the activity under constant darkness subsequent to a light–dark cycle was more intense in the active phase continuing from the scotophase than from the photophase of the preceding light–dark cycle; this indicates the presence of circadian components. These results suggest that two clock systems are involved in controlling locomotor activity in mangrove crickets.

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Locomotor activity rhythm was examined at various temperatures under a 16 h light : 8 h dark photoperiod (LD 16:8) or LD 12:12 using adults of the burying beetle Nicrophorus quadripunctatus. At 20°C, the locomotor activity of the beetles showed a bimodal daily pattern with two peaks around lights on and lights off under both photoperiods. This bimodal activity rhythm persisted under constant darkness; therefore, the activity of adult N. quadripunctatus is controlled by a circadian clock. Adults showed a bimodal activity pattern for temperatures ranging from 15 to 25°C. The evening peak of the daily activity was earlier at lower temperatures. These findings suggest that in the field, N. quadripunctatus shows crepuscular activity, and is active earlier in the afternoon in cooler seasons. In this species, therefore, temperature appears to play an important role in the determination of daily activity patterns.