It’s a well-known nuisance: as soon as an apple or a pear develop a slightly rotten spot, small flies start buzzing around it. No surprise! Fruit flies and their larvae prefer rotting fruit. Researchers at the University of Fribourg have now discovered how these tiny creatures can actually detect when fruit is decaying.

Fly larvae can not only taste food but also perceive its texture – using the same taste cells, known as mechanoreceptors. This was the finding of a study conducted by Prof. Simon G. Sprecher and PhD student Nikita Komarov at the University of Fribourg, which has just been published in the open-access journal PLOS Biology. The research demonstrates that the taste neurons of fly larvae contain mechanoreceptors that detect texture.

Both taste and texture matter
Many studies on food perception focus on tastes such as sweetness or saltiness. However, food preferences often depend on texture as well. For example, some people enjoy the taste of mushrooms but dislike their rubbery feel when chewed. While tasting flavors requires chemical perception, detecting textures involves mechanical perception. Until now, it was unclear whether taste organs, such as the tongue, have the ability to perceive both. This study specifically addressed this question by using fruit fly larvae—commonly known as maggots—since their nervous system is relatively simple and numerous genetic tools are available for research.

Ideally, really rotten
The researchers found that maggots are rather picky eaters and do not eat food that is too hard or too soft. They only consume food when it has the right consistency, which in this case means fruit that has been rotting for a few days. Assuming that this ability to sense food texture is located in the peripheral taste organs, the scientists selectively disabled these taste neurons in the larvae's mouths. As a result, the maggots lost their ability to sense food texture and tried to eat food that was either too soft or too hard – something they would normally avoid. Further experiments showed that the so-called painless mechanoreceptor gene is essential for this perception.

The researchers also discovered that a specific nerve cell—known as C6—in the taste organ of the fruit fly larva detects both chemical stimuli, such as sugar, and mechanical stimuli, such as the hardness of an apple. This nerve cell is therefore capable of recognizing both chemical and mechanical information.

Whether human taste buds have the same capabilities has not yet been studied, says Prof. Sprecher. The biologist is convinced that further research in this area will be of particular interest to the field of nutritional science.

Study
Nikita Komarov, Cornelia Fritsch, G. Larisa Maier, Johannes Bues, Marjan Biočanin, Clarisse Brunet Avalos, Andrea Dodero, Jae Young Kwon, Bart Deplancke, Simon G. Sprecher (2024). Food hardness preference reveals multisensory contributions of fly larval gustatory organs in behaviour and physiology https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002730