While I can't help with the diatomaceous earth question I can relay what I do for the small flying critters.

First off a thick layer of bedding over the top will help. If there is no exposed food there is nothing to attract them and keep them. Any eggs that do hatch will be trapped under the bedding. It is a long term solution but will work with patients.

Do you have a sewing machine? I made a bonnet out of thin sheer fabric and some elastic band to fit over the top of my bin. This will still allow for air but exclude the movement of gnats and flies. Look at the worm inn and see how it has a zip close top. This won't stop an infestation but will keep them from invading the house. At times I have taken my whole bin outside and opened the top to let numerous flies out to die in a northern Illinois winter.

What I read so far, DE will not kill gnats. I have bought hypoapsis mites from The Bug Factory once.

http://www.thebugfactory.ca/pages/products/hypoaspis/?phpMyAdmin=qvaIcfZWsq4X1j5Qpdh%2Cjgi19z2

It reduced the amount of gnats I had but then there are always new ones coming from somewhere. The h. mites should be able to live and become part of the bin population but that doesn't seem the case in my bins. You can also buy nematodes.
My solution: I built a wooden larger bin and consolidated the RM and it's outside. Buying the h.mites or nematodes is getting too costly.
If you can't move the bins outside, mr_yan's suggestion is a good one. I have noticed that gnats can still crawl out of the tiniest opening around the lid though.

Hang a no-pest strip near the bin. Read the cautions on the package before using this solution.

mr_yan said on Sun, Jan 27, 13 at 12:25

... Do you have a sewing machine? I made a bonnet out of thin sheer fabric and some elastic band to fit over the top of my bin. This will still allow for air but exclude the movement of gnats and flies. Look at the worm inn and see how it has a zip close top. This won't stop an infestation but will keep them from invading the house. At times I have taken my whole bin outside and opened the top to let numerous flies out to die in a northern Illinois winter.

I do pretty much the same as mr_yan including setting them free outside in the winter. I don't sew but used curtain sheers (they're cheaper than netting), tape and a stapler to create a large netting bag to totally inclose my RubberMaid tote bin. I also have sticky traps inside the netting to capture the gnats.

Here is a link that might be useful: Curtain Sheers Gnat Netting

tulips101 asked on Sun, Jan 27, 13 at 9:55

Could some one help me by telling me how to use diatomasius earth on my worm bins the knats are starting to get out of hand im new at this.

Just read this on another forum:

"What I mean by "diatomaceous earth interior lids" is a cut a piece of cardboard to fit with handles inside my worm bin to place on top of the bedding, and I cover that with diatomaceous earth."

Here is a link that might be useful: EasyVermicomposting.com

boreal_wormer: looks like access to EasyVermicomposting.com is for paid members only.
PS: I checked out your web site. Very nice and impressive detailed documentation. Thanks for sharing.

This post was edited by otis11 on Mon, Jan 28, 13 at 15:52

I do not know that DE would help at all. The only reason it would is if spread thick enough it would provide a dry barrier over the top. I would not spend money on the bin for parasites. I like the ideas the posters so far have had. You can also flip over the bin so the bottom material is on top and the freshly laid eggs are now at the bottom. I find I can just put the curtain over the top and leave the sides open. For some reason they do not seem to figure out how to fly under it even if it is only a couple of inches draped.

Vacuum the gnats up every day until they are completely gone (can take up to a month, depending on how bad the infestation is). Once the gnats are gone, they say that microwaving the worms' feed before serving can kill gnat eggs (don't know if it's true, but I do it with questionable stuff just in case). I also put my bins in the basement, far away from permeable window screens. Good luck :)

After trying all the other methods, I just hang yellow sticky fly paper above the bins and then ignore them. I find they're more than capable of finding their way to the fly paper all by themselves.

Shaul