Moths may smell the world through their wings, not just their antennae. Scientists at the Max Planck Institute for Chemical Ecology have found that the wings of the tobacco hawkmoth (Manduca sexta) are equipped with odor-detecting receptors and sensory hairs, giving the insects a second, unexpected olfactory system.
"The tobacco hawkmoth was recently found to have receptor proteins in its wings that could detect different smells and tastes," said Dr. Sonja Bisch-Knaden, lead author of the study published in the Journal of Experimental Biology. "But receptor proteins are only the beginning of the sensory cascade that converts scents into nerve signals."
The team gently snipped the edges from hawkmoth wings, sprayed them with a fine mist of gold, and examined them under a scanning electron microscope. Interspersed between slender touch-sensitive hairs, they found stubbier, porous hairs — the hallmarks of scent sensors.
They also collected mRNA from the wings, identifying mRNA for 33 taste and scent receptors, with mRNA for 15 receptors produced along the wing's edge, where the odor-sensing hairs sit. Cross-referencing the receptor proteins with the odors they detect in other insects suggested the wings sense bitter flavors and the aroma of amines — which smell like rotting fish to humans.
To test which scents the wing could actually smell, the researchers rigged a wing to an electrical circuit and blew puffs of odors onto it — from putrid pyridine and fruity methyl hexanoate to the heady scent of Datura flowers. Surprisingly, the wing picked out only two: pyrrolidine and piperidine, both stinky amines found in the leaves of nightshade plants, where tobacco hawkmoths prefer to lay their eggs.
Even more surprising, when the researchers trimmed the edges off the wings and retested, the wings could still detect the unpleasant amine odors. "This suggests that the moth has special sensory hairs across its wings, not just along the edges, that can smell those odors," Bisch-Knaden said.
