How do flies decide what to eat?

We’ve all seen flies swarm to dung or dead animals to eat. Despite the difference in taste between the average fly and most people, the insects don’t eat just anything – their diet has to meet certain criteria. Like all animals, flies spend time seeking out foods that are tasty and nutritious. 

In a new study from Yale University, researchers have investigated the food choices of flies to determine what goes on in their brains while choosing between two menu items.

The experts offered fruit flies (Drosophila melanogaster) two choices – a nutritious food laced with a bitter substance and a less nutritious, low-calorie option that tasted sweet. 

The team used neuroimaging to track neural activity as the flies made the choice between the high-calorie or tasty food.

“It depends on how hungry they are,” explained study senior author Professor Michael Nitabach. “The hungrier they are, the more likely they will tolerate bitter taste to obtain more calories.”

However, the experts report that the real answer to how flies make food choices is a little more complicated. The researchers explained that flies relay sensory information to a portion of their brain called the fan-shaped body, where signals are integrated, triggering what amounts to the insect version of an executive decision.

The study revealed that patterns of brain cell activity in the fan-shaped body change when new food choices are introduced, and this controls the fly’s decision over what food to eat.

The researchers took the study one step further by manipulating neurons in parts of the brain that feed into the fan-shaped body. By decreasing the activity of neurons that regulate metabolism, the scientists were able to force the flies to “decide” to eat the lower calorie food, even when very hungry. 

The reward systems in the brains’ of flies and humans are similar and this study relates to how Homo sapiens make food decisions as well. In this way, this finding could be used as a way to understand how hunger and eating behavior work in humans.

“The study provides a template to understand how it is that things like hunger and internal emotional states influence our behavior,” said Professor Nitabach.

The study is published in the journal Nature Communications.

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By Zach Fitzner, Earth.com Staff Writer