Interaction of visual and olfactory cues in the aggregation behaviour of the haematophagous bug Triatoma infestans

We analysed how the assembling behaviour of Triatoma infestans is modulated by the convergence of chemical cues released by their faeces and the spect ral quality of the light associated with refuges. Second-instar larvae were confronted with refuges associated with a visual stimulus (either blue, gr een or red lights having the same intensity, or darkness) and a chemical cu e (presence or absence of faeces). In this context, faeces constitute a maj or attractant for bugs. In the absence of faeces, bugs always assembled in dark places. Green light was always rejected despite the presence of faeces , i.e. the assembling behaviour was controlled by a photonegative reaction to this light. In the presence of red light, orientation towards the chemic al cue dominated over the bugs' photonegative reaction to this light. Such a light was avoided in the absence of faeces but not in their presence. Als o, negative phototaxis to blue light could be counteracted by the presence of the chemical cue. Thus, a concrete interaction between visual and olfact ory cues occurred in these experiments: the bugs' response changed dependin g on the specific combination of spectral light and faeces. Finally, bugs r esponded differentially to blue, red and green lights of the same intensity . They assembled preferentially on red, followed by blue and then by green. Thus; discrimination between lights of different spectral quality is possi ble, probably through an achromatic mechanism.