Could it be that your expert has mistaken adult fungus gnats and their worm like larvae for fruit flies? This is a common mistake for the novice.

Fruitflies are not likely to pester house plants, but fungus gnats do. They lay their eggs into the potting mix and the little larvae feed upon organic debris (like peat moss) and tender plant roots.

I meant to add...be sure to reply back to this thread and verify the fungus gnat situation and we can provide assistance in controlling them. It will have nothing to do with nematodes, by the way, lol.

Many people mistakingly call Fungus Gnats Fruit Flies but you only find Fruit flies where you have overripe fruit and not around house plants. Fungus Gnats are one of the more common house plant pests the Master Gardeners on hotlines encounter and the major reason is people tend to overwater their house plants.
Yellow sticky traps can help control Fungus Gnats by attracting the adults, trapping and holding onto them so they cannot lay eggs in the potting soil, but the best means of control is to allow the potting soil to dry out between waterings.

Here is a link that might be useful: Fungus Gnats