The chemosensory ecology of a foraging hawkmoth
While foraging, all animals need to balance their energetic cost and gains. The sensory systems provide the information, which form the bases for these energy-economic decisions and thus, link the sensory input directly to the fitness of the animal. Night-active hawkmoth species particularly rely on their olfactory system which detects the volatiles emitted by those plants visited by the moth. This dissertation examined the olfactory system and the foraging decisions of the hawkmoth Manduca sexta to gain further insights into the ecological pressures which might have directed the evolution of the olfactory system in hawkmoths and their coevolution with the flowers they visit. In order to address these questions we first studied the odour guided flight of M. sexta to flowers of different Nicotiana species, which matched the length of the moth proboscis to different degrees. It was found that the moth already selected the best matching flower at the first encounter with the odour plume emitted by this flower and that foraging on these matching flowers did result in the highest energy gain for the moth. We could further show that M. sexta recognise a plant headspace based on the composition of this blend rather than on its concentration. However, flower odours are readily intermixed with other volatiles and their detection is hence most reliable close to the flower. Here, we show that the moth uses specific olfactory neurons on the tip of its proboscis to evaluate flowers, and that this close range detection is crucial both for foraging as well as pollination. Finally, the effect of flower orientation on the foraging of M. sexta was analysed, finding that the synchronisation of floral volatiles and orientation is crucial for this moth-plant interaction. Taken together our studies on the foraging of hawkmoth might not only help to gain new insights into the evolution of sensory systems, but also on how these systems shapes the interaction between different species.
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