Circadian rhythm of locomotor activity in the bed bug, Cimex lectularius

The bed bug, Cimex lectularius, must avoid detection when finding its hosts and returning to hidden harborages. Its stealthy habits include foraging when its hosts are asleep. Characteristics of its locomotor activity rhythm were studied by recording positional changes every 10 minutes. In the absence of host stimuli, both adults and nymphs were more active in the dark than in the light. Locomotor activity persisted but gradually decreased when insects were kept under constant dark (DD) or constant light (LL) conditions. The persistence of the recurring activity pattern under continuous conditions revealed the existence of an endogenous circadian rhythm. The free-running period for all stages was longer in DD (25.0 h) than in LL (24 h for females and nymphs, and 23.6 h for males). The lengthening of the free running period in DD is an exception for the circadian rule that predicts the opposite in nocturnal animals. The frequency of positional changes was associated with the feeding status. As expected, unfed young adults moved more frequently than recently fed adults of the same age (one to two weeks old). While bed bugs can survive for a year or more without a blood meal, we observed a reduction in activity in insects held for five-weeks without food. We suggest that bed bugs make a transition to host-stimulus dependent searching when host presence is not predictable. Such a strategy would enable bed bugs to maximize reproduction when resources are abundant and save energy when resources are scarce.