The kitchen has a bunch of fruit flies in it, and apparantly they are coming from (or at least feeding on) the hole in the top of this banana. Based on their light color I suspect these are very young fruit flies, so they are probably breeding in there as well.
After sealing it in a zip-top bag I’ve thrown out the remaining bananas, but not after taking the most-rotted upper section and putting it in a pint glass, covering the top with foil, and piercing it with a toothpick (photo). Hopefully this will work nicely as trap for the remaining flies that seem to be lingering in the area. Ten minutes or so have passed since I assembled the makeshift trap and it already contains four flies, so it looks promising.