Do soil-less medias have a natural defense against gnats?

Last year I used 50/50 mix of perlite/vermiculite in the cup stage in a humidity bin.  After potting up to 2 gal, they went outside.  I never saw a single gnat, and kept wondering what was the big deal about them after reading everyone elses horror story.

So far this year, after rooting, they've gone directly to 32oz mini sips using a 50/40/10 mix of perlite/mg potting mix/cow manure compost.  Ever since, I've been growing more gnats than trees. And can't get rid of them.  Been using gnatrol for every watering for over a month.

I'm thinking the larvae must have already been in the mg potting mix or manure?  Or are they just drawn to that type of mix more?

I moved everything to the garage about 4 weeks ago, so my office upstairs should be free of them by now. I'm going to try again using the vermiculite while indoors and back in the humidity bin.

I have started to Microwave my potting mix a little at a time to reduce the Gnat problem. I also have all my cuttings covered with a ziploc bag with 2 small openings for air. I keep a good eye out and if I see a gnat on the top of the bag, I smash them...LOL    I have also put them in 1 gal. pots, not using cups anymore and more soil content. The Soil seems to give nutrients and lock in moisture. So having better success at the moment.

I might have to buy a microwave for the garage then.  There's no way in h311 my wife will let me put potting mix in the kitchen microwave.

cow poop might have had gnat larvae/egg.. you see funny cartoon with flies all over cow pie? they also lay eggs on them. 

Be Careful on what you microwave. Cow manure is probably not good to put in the microwave...LOL     I have put some potting soil in the freezer for a few days, not sure if it killed the larvae..???   

it is possible the gnats came with the cuttings. I've received cuttings from one source three different years. each time I had a problem with gnats and death caused by rot. Last year I used the root riot cubes. The cubes with cuttings from this source had gnat larvae crawling around in them. The others did not.

James,
Soil-less media (perlite, vermiculite and raw compressed peat) typically do not have spores and fungus Gnats.
 
Compost, Garden Soils, Potting Soils, Manures or Solid Organic Fertilizers in the cutting mix attract or may introduce Fungus Gnats and microbes, they are attracted to Damp Soil and Fungus, where they lay their eggs. If you eliminate these, Fungus Gnat infestation will decrease dramatically. If you try to keep your cutting mix as sterile (clean) as possible, you will reduce or eliminate infestation and sources of rot causing microbes. Good Luck.

I guess grape, blueberry or orange scented nail polish isn't a good idea though.   At least my daughter's cosmetics are safe. 

hmm.. i have to think about this. my wife wear stuff on her fingernail that gnats will even avoid?