Research has shown that not only can antioxidants be 'indirectly' smelt by fruit flies, but the substances attract the pest and causes them to increase their feeding behavior.

Vinegar flies on a cherry

Antioxidants are natural food ingredients that protect cells from harmful influences. Their main task is to neutralize so-called 'free radicals', which are produced in the oxidation process and are responsible for cell degeneration.

Scientists at the Max Planck Institute for Chemical Ecology in Jena, Germany, and the University of Lund, Sweden, have now shown that vinegar flies are able to detect these protective antioxidants by smelling the chemical they release when they metabolize.

Odors that are exclusively derived from antioxidants not only cause the pest to feed more, but also cause female flies to lay eggs.

The research came about when scientists decided to take a closer look at a source of antioxidants, hydroxycinnamic acids, that are found in high amounts in fruit.

As fruit is the prefered breeding ground for fruit flies, the scientists sought to discover what possible effects the hydroxycinnamic acids might have on the pest.

The flies cannot smell the antioxidants directly, but instead detect the substance given off when they react with yeast. The substance therefore provides reliable information to the flies of the of antioxidants' presence in the food.

The perception of these signals was found to have a direct impact of the flies' behavior. They are attracted by the odor sources, show increased feeding behavior and choose sites to lay eggs where the substances indicate that antioxidants are present in the breeding ground.

"This form of olfactory proxy detection is not only a phenomenon in insects," scientist Marcus Stensmyr said.

"It has also been shown in humans, that odors that we perceive as pleasant or appetizing, are in fact derived from important and healthy nutrients, such as essential amino acids, fatty acids and vitamins."

These findings demonstrate a further example of an individual neuronal pathway, which has a profound effect on the flies - from the odorant signal to olfactory neurons and dedicated odorant receptors to behavior.

The pathway as a proxy detection of dietary antioxidants shows yet another facet of the complex odor-guided behavior in fruit flies.

The scientists will now try to identify further neural pathways involved in the detection of essential nutrients, which ultimately trigger the flies' behavior.

Photo: Anna Schroll

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