Thanks a lot, Susanne! We are having light showers in NorCal every other day now and the surface is always moist :(

Will removing mulch somewhat help with this problem?

If yes, is using perlite as a top layer better than organic mulch?

I would think perlite is dry much faster then mulch and maybe a better choice.

perlite tends to not stay where you put it, tho

Oh yes, wind will just blow it away

What about pumice?

It is heavier and, as I understand, it does not absorb a lot of water.

You can also put a little container next to the plant with vinegar and a drop of soap, they would drown in there or buy sticky stakes

Some people also hang up sticky tape I've heard. When hirts shipped my red lime tree, the pot was covered with tape for shipping to keep the dirt from spilling. I was thinking, if I ever had a fungus gnat problem I may try to tape up the pot to see if gnats would stick to the tape. I wonder if that would work at all? Luckily I haven't had a gnat problem for a long time now. Watering less solved the problem.

When I got mine from a bad load of potting soil had to go with the full guns to eradicate them. I grow indoors and prob harder to get rid of- I hope you don't have them to the extent I did. One thing is that the adults do no damage. It's the larvae in the soil that nibble roots, and the adults lay those eggs once a week. I ended up cutting back on water, using neem oil, gnatrol, and the yellow sticky tape- but only the kind that can be poked in the soil. The gnats hang out in the top layer of the soil and the so hanging the tapes on the branches is less effective. If you don't kill the larvae you won't have complete control. Took me 3 months to get fully rid myself of them. I hope just the first steps and getting rid of the mulch will be all you need.

I removed the mulch and it helped I guess. I still see them but definitely not as many. I am not going to water the affected trees (Clementine, Meiwa and Meyer) for 7-8 days to kill/reduce the larvae. Unfortunately, we are having a light shower on Monday :(