ISLAMABAD  - When fruit flies are hungry, they become better in scenting out their next good meal. "As humans, we sometimes forget that feeding behaviour has two components," said Jing Wang of the University of California, San Diego, who led the study.

"First, you have to go out and hunt for food," Wang said, adding that actually eating that food is secondary, reports the journal Cell.

As our experiences suggest, during hunger the fragrance of food becomes even more delectable. Likewise, food that smells especially good is also especially hard to resist.

Wang and colleagues set out to study what happens to flies' sense of smell after they were starved for a few hours, according to a California statement.

Insulin in flies works in essentially the same way as it does in humans, Wang said. It controls the amount of sugar in the circulation. "When a fly is hungry, insulin drops dramatically. This tells the olfactory neuron to change its sensitivity."

That change is controlled on certain neurons (nerve cells) through an increase in the activity of the gene encoding the neuropeptide F receptor.

With more receptors on their surfaces, those neurons grow increasingly sensitive to the neuropeptide and to the odour cues they are designed to pick up. 

As their name implies, fruit flies forage on rotten fruits, Wang says, and it is the neurons that pick up the vinegary scent of fruit decay that is affected.

The shift in sensitivity reaches its peak in about four hours, a fact that Wang said he found intriguing in part because it mirrors the typical spacing of our meals - breakfast, lunch and dinner.

After all, not all animals are episodic feeders like we humans are. Some animals eat all the time and others eat only very infrequently.