ORIGINAL PAPER What matters in the associative learning of visual cues in foraging parasitoid wasps: colour or brightness? Emmanuel Desouhant • Simon Navel • Emmeline Foubert • Deborah Fischbein • Marc The ´ry • Carlos Bernstein Received: 8 September 2009 / Revised: 3 December 2009 / Accepted: 4 December 2009 / Published online: 18 December 2009 Ó Springer-Verlag 2009 Abstract Visual cues are known to be used by numerous animal taxa to gather information on quality and localisa- tion of resources. Because environmental lighting can interfere with the spectral features of visual cues, the specific characteristics of the colour signals that promote forager decision and learning are still not known in the majority of insects (excepted in bees). We analysed the effect of previous experience on the use of visual infor- mation by the wasp Venturia canescens, a parasitoid of pyralidae, in the context of host searching. These parasit- oids search for hosts concealed in several fruit species, so visual cues from the host microhabitat could play a key role in host finding. We also investigated the type of visual cues on which wasps based their decision. We tested whether wasps are able to associate an achromatic cue (brightness) or a chromatic one (hue, i.e. dominant wavelength and/or chroma) with the presence of hosts. Our results show that in the context of host foraging, chromatic cues are more reliable than brightness in achieving the associative learning process. Therefore, understanding the behavioural ecology of foraging should make use of the knowledge about the visual information used. Keywords Hymenoptera Á Venturia canescens Á Host foraging Á Colour contrast Á Brightness contrast Á Cognitive ecology Introduction Visual cues or signals are involved in numerous decision- making processes in contexts such as foraging (Schmidt et al. 2004; Raine and Chittka 2007) or mate choice (Baeder and King 2004; Uy and Endler 2004), both in vertebrates and invertebrates. The use of this visual infor- mation is expected to reduce the uncertainty of the con- ditions in the environment and leads to adaptive behavioural responses to variability. Informative examples of evolutionary consequences of decisions based on visual cues are the co-evolution of plant–insect interactions (Shafir et al. 2003), speciation via mate choice (Gray and McKinnon 2007), and the evolution of display behaviour in mate choice (Endler and The ´ry 1996). Detection and the use of colour cues might be influenced by the environmental context in which the colours are expressed. Indeed, the light spectrum that reaches the viewer’s eye from a colour object depends on the ambient light spectrum reaching the object, the object’s reflectance spectrum and the transmission spectrum of the environ- mental medium (Endler 1993). Consequently, the colour of an object can vary depending upon when and where it is viewed. For instance, in some insect pollinators, the light availability directly influences behaviours: plants in the sun receive more visits than plants in the shade, independently E. Desouhant Á S. Navel Á E. Foubert Á C. Bernstein Universite ´ de Lyon, 69000 Lyon, France E. Desouhant (&) Laboratoire de Biome ´trie et Biologie Evolutive, Universite ´ Lyon 1, CNRS, UMR 5558, Bat G Mendel, 69622 Villeurbanne, France e-mail: desouhan@biomserv.univ-lyon1.fr D. Fischbein Laboratorio de Ecologı ´a de Insectos, INTA Bariloche, CC 277, 8400 Bariloche, Argentina M. The ´ry De ´partement Ecologie et Gestion de la Biodiversite ´, Muse ´um National d’Histoire Naturelle, CNRS UMR 7179, 1 avenue du petit cha ˆteau, 91800 Brunoy, France 123 Anim Cogn (2010) 13:535–543 DOI 10.1007/s10071-009-0304-2