I've been battling fungus gnats for most of the winter.  At first I only thought of them as a nuisance, but eventually I learned that they're eating the roots and inner bark of the very cuttings I'm trying so hard to grow!  I went on the offensive with various aspects of biological, chemical and physical warfare, but so did they.  Yes, there have been many casualties on both sides.  (The last battle was like a scene out of Starship Troopers!)
    I've cursed the little buggers and their translucent little wormy children for the damage they inflicted.  I've un-cupped once-promising rooted cuttings only to find shriveled brown rootlets and mushy, rotted-out gunk where healthy wood used to be.
    Now I'm wondering how much of the damage was REALLY caused by the gnat larvae?  Or is it as likely, or even more likely, that the cuttings started going south on their own?  Maybe the rotting of the wood started first and the gnat larvae moved in to make the best of good (for them) situation.  I'm a new fig grower, so it is very likely that I've given some of my cuttings various combinations of too-wet, too-dry, too-hot and/or too-cold conditions at one time or another.
    Or am I giving these guys the benefit of the doubt too much?  The larvae eat roots, inner-bark and fungus.  They don't eat rotted fig-wood per se.  But is it the rotting wood/bark that is helping to attract them to a given cutting....or are they causing the rot by eating the roots and inner bark?  Which came first, the fungus or the gnat?!?!?!
Jim   

Tell me about it! I hate these monsters. Must hide the cuttings from them if all possible. I monitor them in moss, as they  fly in without you seen them. I check them everyday, and when I put them in cups, they go inside of containers that I can put fabric and a sealed lid that allows the fabric to breathe until their roots get stronger.  Sadly, I;ve got some insect killer that  is powder and I put on top of the soil. I water the cups from the bottom and seal their bottoms inside another cup or plastic bag with a rubber band. Anything to give my cuttings a chance..once they take off, their root systerm recovers, but not when they are so young.  I am totally with you on this battle. trap the adults and soap the babies, water from the bottom, so adults are discouraged to lay eggs in the dry soil.. ok to let it be very dry on top.

Just as an observation, I had the same battle going on in my house all winter with many losses...you could actually see the gnats hovering over the plants, and not only that, but they were flying all over the house...you couldn't even read the news paper without one of them flying in your face...OK, I said all that to say this, on March 1st. (39 days ago) I set up my first root riot tray...in addition I have set up two more trays since that time...that's 150 rooted and leafed out cuttings "with no sign of any fungus gnats"...I spray the cuttings twice a day under the humidity domes, so there's lots of humidity trapped in there, yet no gnats...one possible conclusion that I am comming to is that there is no "soil" involved in the process...the root riot cubes are made of bio-degradable organic material (don't know what that means), but the bottom line is that since I switched over to root riot cubes, the gnats are gone.  :)  :)