ORIGINAL PAPER Carolina E. Reisenman á Alicia N. Lorenzo Figueiras MartõÂn Giurfa á Claudio R. Lazzari Interaction of visual and olfactory cues in the aggregation behaviour of the haematophagous bug Triatoma infestans Accepted: 21 August 2000 / Published online: 13 October 2000 Ó Springer-Verlag 2000 Abstract We analysed how the assembling behaviour of Triatoma infestans is modulated by the convergence of chemical cues released by their faeces and the spectral quality of the light associated with refuges. Second- instar larvae were confronted with refuges associated with a visual stimulus either blue, green or red lights having the same intensity, or darkness) and a chemical cue presence or absence of faeces). In this context, faeces constitute a major 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 chemical cue domi- nated over the bugs' photonegative reaction to this light. Such a light was avoided in the absence of faeces but not in their presence. Also, negative phototaxis to blue light could be counteracted by the presence of the chemical cue. Thus, a concrete interaction between visual and olfactory cues occurred in these experiments: the bugs' response changed depending on the speci®c combination of spectral light and faeces. Finally, bugs responded dierentially 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 dierent spectral quality is possible, probably through an achromatic mechanism. Key words Triatomines á Assembling behaviour á Phototaxis á Vision á Olfaction Introduction Insects employ a variety of dierent sensory modalities to guide themselves, and to identify an appropriate object or condition Dusenbery 1992). Visual, olfactory and mechanical signals are commonly used by insects for locating food, oviposition sites and mates Bradbury and Bennett 1974). Co-occurrence of signals of dierent sensory modalities results in multimodal convergence, i.e. in the uptake of information by functionally dierent sense organs and the resulting interaction at dierent levels of the sensory pathway Horn 1985). Such an interaction can occur at the receptor level, in ascending or descending neurones, or even in motoneurons. Usually multimodal convergence elicits speci®c behavioural reactions. Sometimes animals respond only if a speci®c pattern of sensory cues takes place, but in other cases some cues are predominant. Host location in haematophagous insects is an inte- grated response driven by dierent sensory cues Lehane 1991). Multimodal responses in haematophagous insects have a high adaptive value because they improve the chances of host ®nding Lehane 1991). These insects use mainly visual, olfactory and thermal signals in their search for food Bradbury and Bennett 1974; Warnes and Finlayson 1985; Allan et al. 1987; Lehane 1991). This fact has been used in the control of insect vectors: for instance, coloured targets baited with host odours CO 2 ) are more ecient in capturing tsetse ¯ies than coloured targets lacking odour Green 1986, 1993). Triatoma infestans is a haematophagous insect which has a fundamental epidemiological importance in South America as it is the main vector of Chagas disease. Adults and larvae of this bug are domestic in habitat. They exhibit a strong negative reaction to light Rei- senman et al. 1998) and spend daylight hours assembled in shaded places inside wall crevices. The aggregation C. E. Reisenman &) á A. N. Lorenzo Figueiras á C. R. Lazzari Laboratorio de FisiologõÂa de Insectos, Departamento de Ciencias BioloÂgicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, C1428EHA) Buenos Aires, Argentina e-mail: carolina@bg.fcen.uba.ar Tel.: +54-11-4576-3300 ext 332; Fax: +54-11-4576-3384 M. Giurfa Neurobiologie, Institut fuÈr Biologie, Freie UniversitaÈt Berlin, KoÈnigin-Luise-Str. 28/30, 14195 Berlin, Germany J Comp Physiol A 2000) 186: 961±968 DOI 10.1007/s003590000149