Approximately 1 day after eclosion, the imago of the hummingbird hawkmoth Macroglossum stellatarum starts searching for nectar sources. How does it find the first flower? Like other flower-visiting insects, it must be guided by means of an innate flower template (Darwin, 1877). The template may contain various features, such as odour (see Knoll, 1925, 1926; Ilse, 1928), colour (Lepidoptera: Ilse, 1928; Swihart, 1971; Scherer and Kolb, 1987a,b; Cutler et al. 1995; bumblebees: Lunau, 1990; Lunau et al. 1996; honeybees: Giurfa et al. 1995b; hoverflies: Ilse, 1949; Lunau and Wacht, 1994) and flower size and pattern (Lepidoptera: Ilse, 1933; honeybees: Lehrer et al. 1995). Analysing spontaneous preferences is interesting for two main reasons. First, it is a very useful method for studying animals that cannot easily be trained to a particular stimulus, such as crickets (Campan and Lacoste, 1971) and beetles (Varjú, 1976; Dafni, 1997). In several lepidopterans that cannot easily be trained to flower colours, the feeding response has been described using this technique as a wavelength- specific behaviour, the sensitivity of which depends mostly on the blue, and to a lesser extent on the green, receptor (Scherer and Kolb, 1987a,b; Cutler et al. 1995). In different contexts, the same animals might perform different wavelength-specific behaviours or even demonstrate true colour vision, as has been shown in the case of the honeybee (Menzel, 1979). Second, spontaneous choices might tell us which sensory cues are behaviourally important in the environment. Giurfa et al. (1995b) gave an ecological explanation for innate colour preferences: they have shown that honeybees are guided to flowers that promise a large amount of nectar. Lehrer et al. (1995) analysed pattern preferences in the same insect and concluded that flower-like patterns are preferred to others. They did not, however, work with flower-naive bees. The day-active hummingbird hawkmoth Macroglossum stellatarum is attracted by visual stimuli alone, although odours may also influence its motivational state (Brantjes, 1973). In contrast to other species (Knoll, 1926; Ilse, 1928; Brantjes, 1973; Scherer and Kolb, 1987b), this influence is not necessary to induce feeding behaviour in M. stellatarum (Knoll, 1922). Despite the fact that no electrophysiological recordings from its photoreceptors exist, it can be assumed that M. stellatarum has three spectral receptor types with 827 The Journal of Experimental Biology 200, 827–836 (1997) Printed in Great Britain © The Company of Biologists Limited 1997 JEB0661 The diurnal hawkmoth Macroglossum stellatarum is known to feed from a variety of flower species of almost all colours, forms and sizes. A newly eclosed imago, however, has to find its first flower by means of an innate flower template. This study investigates which visual flower features are represented in this template and their relative importance. Newly eclosed imagines were tested for their innate preferences, using artificial flowers made out of coloured paper or projected onto a screen through interference filters. The moths were found to have a strong preference for 440 nm and a weaker preference for 540 nm. The attractiveness of a colour increases with light intensity. The background colour, as well as the spectral composition of the ambient illumination, influences the choice behaviour. Blue paper disks against a yellowish background are chosen much more often than the same disks against a bluish background. Similarly, under ultraviolet-rich illumination, the preference for 540 nm is much more pronounced than under yellowish illumination. Disks of approximately 32 mm in diameter are preferred to smaller and larger ones, and a sectored pattern is more attractive than a ring pattern. Pattern preferences are less pronounced with coloured than with black-and-white patterns. Tests using combinations of two parameters reveal that size is more important than colour and that colour is more important than pattern. Key words: Macroglossum stellatarum, hawkmoth, Sphingidae, Lepidoptera, spontaneous choices, innate behaviour, colour vision, pattern vision. Summary Introduction INNATE PREFERENCES FOR FLOWER FEATURES IN THE HAWKMOTH MACROGLOSSUM STELLATARUM ALMUT KELBER* Lehrstuhl für Biokybernetik, Auf der Morgenstelle 28, D-72076 Tübingen, Germany Accepted 29 November 1996 *Present address: Centre for Visual Sciences, Research School of Biological Sciences, Australian National University, PO Box 475, Canberra, ACT 2601, Australia (e-mail: Almut.Kelber@rsbs-central.anu.edu.au).