Circadian control of photonegative sensitivity in the haematophagous bug Triatoma infestans

The negative phototactic response of Triatoma infestans (Hemiptera) was studied in an arena, half of which was kept dark and the other half illuminated with different light intensitites. For each intensity we measured the time the insects spent in the dark half, the time to reach the side opposite to that where they were released, and the number of passages through the middle line of the arena. T. infestans displayed a photonegative behaviour that was enhanced by high light intensities. Bugs maintained in 12:12 light-dark cycles responded differently to the same illumination levels when tested in their photophase and scotophase: sensitivity to light was higher during the latter. Bugs entrained to light-dark cycles, kept afterwards either in constant darkness or in constant light, and tested in their subjective night and day, showed the same responses as bugs from the light-dark group tested in their corresponding photophase and scotophase. Thus, phototactic sensitivity is under endogenous control. The behaviour shown by T. infestans may be understood as being composed of at least two different drives: an exploratory one, and a negative phototactic response that is under endogenous control and is particularly sensitive to light during the scotophase, when activity peaks occur.