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Tobacco hawkmoths are incredibly sensitive to important smells

Nocturnal tobacco hawkmoths (Manduca sexta) use their keen sense of smell to find nectar rich flowers or plants on which to lay their eggs. Now, researchers at the  Max Planck Institute for Chemical Ecology are looking to answer the question of how the moths distinguish between different smells. 

With so many smells in the world, how can moths pick out those that are essential for their lives from those unnecessary whiffs?  

“Our question is based on the fact that the plants that are vital for the tobacco hawkmoth, that is nectar sources and suitable host plants for their offspring, are very sparse in their natural habitat. Apparently, however, these plants are nevertheless found by the moths. We wanted to know whether the olfactory system can also filter out weak odor signals if they provide the moths with clues that lead them to food sources or oviposition sites,” said Sonja Bisch-Knaden, lead author of the study.

To carry out the research, the scientists collected scents from 17 different plants in Arizona. These plants were reported to be important to the moths and the scents were carefully collected at night, when the hawkmoths are active. 

As the moths were exposed to different scents, the researchers observed their antennae and brain activity. The researchers compared virgin female moths and mated female hawkmoths to see if there was a difference in scent sensitivity. Calcium imaging was used to visualize the neuron activity as moths were exposed to smells. 

“The most important nectar sources, such as agave and datura flowers, give off a strong odor to which the antennae and brain of a female tobacco hawkmoth also respond more strongly than to any other odor. Here, identification of the floral scent appears to be straightforward. This applies to both virgin and mated females, as the few host plants of the larvae are widely scattered throughout the habitat, and the egg-laying female must therefore travel long distances and refill her energy reserves constantly,” said Bisch-Knaden.

“In contrast, host plants as oviposition sites have only a very weak odor, but individual odor components are nevertheless recognized by the antennae. The activity patterns that these odors evoke in the brain are very different from the activity patterns of other plant odors.” 

“This difference becomes even greater after mating, as the female is then virtually unaware of the odor of the other plants that are not candidates for egg-laying. It is still difficult to explain how the moths find these plants in nature on the basis of their odor alone, since the plant odors cannot be perceived individually, as in our study, but always in a mixture.”

The research published in the journal eLife, is just the beginning. The scientists hope to next compare their results to those with related species of moths. 

By Zach Fitzner, Staff Writer

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