New research from the University of Arizona at Tucson reveals how moths key into the scents of flowers. Though a flower's odor may consist of hundreds of chemicals, a moth only pays attention to a small subset of chemical cues as it forages. The research, led by Jeffrey A. Riffell, showed how the moth brain processes a specific smell from the stream of scents it encounters in the air.
Tobacco hornworm moth, Manduca sexta, sucks nectar from its favorite nectar source, the flower of sacred datura, Datura wrightii.
Photo by Charles Hedgcock RBP
The UA team used tobacco hornworm moths, Manduca sexta, and its preferred source of nectar, flowers of the sacred datura, Datura wrightii, to test the neural responses of the moths to different chemical odors. The study marks the first time researchers have used individual chemicals captured from real flowers, rather than synthetic odors, to map responses in insect brain activity.
Datura flowers emit over 60 different chemicals, but only nine of the odors provoked a neural response in the tobacco hornworm moths. Even more intriguing, all nine of these odors had to be present simultaneously before the moth would fly to the source of the smell and attempt to collect nectar.
Riffell devised an ingenuous way to collect the fragrance of a datura flower. He engulfed a flower with a Reynolds® Oven Bag and sucked the air out of the bag and into a charcoal filter. The odor chemicals were thus trapped on the filter. In the lab, Riffell created a solution of the chemicals and injected it into a gas chromatograph. The chromatograph separated the chemicals.
Capturing the scent of a sacred datura flower, Datura wrightii.
Jeffrey A. Riffell
Each individual chemical traveled down a branched tube, with one branch leading to a moth wired to measure brain responses, and the other branch to a machine that identified and recorded the chemical. Recording equipment hooked to a speaker produced an audible popping sound when the moth's brain reacted to a chemical. Researchers could then correlate the responses to the chemicals identified by the machine. Nine times, the scientists heard the pop-pop-pop that indicated a neural response.
Finally, the team studied how the moths would behave toward these chemicals. Using synthetic versions of the chemicals, Riffell and his colleagues created artificial flowers made of white filter paper. The paper flower was placed at the end of a wind tunnel, with a moth at the other. When the paper flower offered just one of the nine chemicals, the moths were indifferent to them. But as soon as all nine chemicals were introduced simultaneously, the moths flew right to the flower and attempted to forage.
Tobacco hornworm moth, Manduca sexta, seeks nectar from an filter-paper flower soaked in some chemicals from the scent of its favorite nectar source, the sacred datura flower, Datura wrightii.
Photo by Charles Hedgcock RBP
"It was amazing -- as soon as you combined the chemicals, the moth behaved like gangbusters," Riffell said. "It flew upwind to the flower and stuck out its proboscis at the flower."
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