Why sweet flies don't like cold sweets so much?

A pancake with plenty of maple syrup has a sweetness that fills the mouth when freshly baked, but the sweetness is considerably reduced when cooled once. This is not just for humans, but for other living things, we know that appetite tends to diminish with cold food. I didn't know much about how cold reduces appetite, but researchers at the University of California, Santa Barbara have figured out the cause of flies.

Temperature and Sweet Taste Integration in Drosophila-S0960-9822 (20) 30436-X.pdf
(PDF file)

Biologists investigate why the sweet taste of sugary foods diminishes when they're cool
https://phys.org/news/2020-04-biologists-sweet-sugary-foods-diminishes.html

Professor Craig Montell of the University of California, Santa Barbara and others wonder whether the fact that `` cold food feels less sweet '' applies not only to humans but also to Drosophila melanogaster , and if so, what is the underlying mechanism? I thought.

Drosophila has one type of taste neuron that senses sugar, and bitterness and texture are sensed by different taste neurons. On the other hand, the sense of temperature is rather complicated, and it will be recognized as 'cold' only when both bitter taste neurons and taste sensation taste neurons are activated. A protein called rhodopsin 6 (Rh6) is involved in this bitterness.

Previous studies have shown that Drosophila melanogaster loses its appetite when food is bitter or hard. The research team conducted an experiment and confirmed that the flies' appetite decreased even when the temperature dropped. However, despite changes in behavior, there was no difference in the activity of taste neurons that sense sweetness.

The researchers confirmed that when Rh6 was removed, taste neurons that Drosophila sense bitterness do not activate at low temperatures. By not activating these taste neurons, flies will not be able to recognize that they are cold, and they will also be attracted to 'cold foods with high sugar content.'

Professor Montell speculates that the reason why Drosophila's appetite decreases when it gets cold in the first place is 'because it reduces metabolism, so it does not require much food.' Humans do not feel the sweetness of cold foods as well, but since they are homeostatic animals, the mechanism found in flies does not apply.