Tobacco hawkmoths are particularly partial to a sip of coyote tobacco nectar. Sniffing the scent of these delicate flowers from afar, the elegant moths are guided by their antennae before hovering in front of the blooms to feast. However, Bill Hansson and Markus Knaden from the Max Planck Institute of Chemical Ecology, Germany, recently discovered that the insects are equipped with a second ‘nose’, perched at the tip of their tongue (proboscis), which is sensitive to the scent of the flowers they frequent. The question was whether the moths’ additional nose contributes to their ability to find the next feast.
Providing the moths with large artificial flowers to dine at, the insects quickly learned to select the fake flowers, especially when they were perfumed with linalool, a key component of coyote tobacco flower scent. Once the insects had got the hang of visiting the scented and unscented artificial flowers, following either their eyes or their antennae, Elisabeth Adam then restricted the guiding linalool scent to the interior of the artificial flower, where it could only be sniffed by the sensors at the top of the moth's proboscis. However, when she checked whether the insects had learned that the scent of linalool – signalling a nectar reward – when sniffing with the proboscis alone, the moths seemed none the wiser. The additional nose at the tip of the moths’ proboscis was unable to guide them to nectar laden flowers. Even when the moths had already learned to recognise the guiding aroma of linalool when directed by their antennae, they were unable to recognise the flower fragrance when sniffing with their proboscis.
The team suspects that the moths’ two ‘noses’ have very different roles. The antennae help the moths learn the scents of the best dining opportunities, in addition to guiding them in the right direction, while the nose at the tip of their proboscis might tell them whether they've found an inferior bloom or a Michelin starred banquet.