Circadian organization of locomotion activity in the haematophagous bug Triatoma infestans

Daily locomotor activity of Triatoma infestans adults exhibits two major components, one at the second hour of the scotophase and a second one at the beginning of the photophase. The occurrence of peaks can be ascribed to food and refuge search at dusk and dawn, respectively. Both maxima appear under discrete light-dark regimes (12 h light-12 h dark, 25:0 lx) at constant temperature, as well as under discrete ligh-low temperature cycles 12 h at 30°C-12 h at 20°C in continuous light or in darkness. Under constant darkness, both maxima of activity display different freerunning periods (τa ≈ 23 h 50 min, τb ≈ 22 h 15 min), suggesting the involvement of two oscillators controlling individually, the two activity peaks. Under continuous light, however, activity becomes unimodal, freerunning at τ ≈ 26 h 40 min. Resetting a 180° shift of high-low temperature cycles occurs faster than by light-dark cycles. In conditions of zeitgeber competition, by simultaneous exposition to light and temperature cycles at various phase relationships, light preponderantly controls the synchronization of activity. Results indicate that the activity of T. infestans is controlled by a circadian system involving a hierarchical arrangement of coupled oscillators. Environmental temperature modulates the activity level and the time course of the spontaneous locomotion. Antennectomy affects the temporal expression of the activity, insects becoming active at an unusual daytime.