How to naturally kill fruit flies?

A DIY fruit fly trap can be a very effective way to deal with a fruit fly infestation.

You'll need the following materials or ingredients.

-a bottle of Apple cider vinegar

-A couple glass jars

-A couple sheets of plastic

-Something to make holes in the plastic. Knife is ok

-A rubber band

Some house-hold dishwashing liquid

Once you have all these items, its time to make your very own traps. All that you need to do is pour about a cup of the Apple cider vinegar into your glass jar and add a tablespoon of dishwashing liquid into the mixture. Give it a single shake to mix the soap into the vinegar and then fit the plastic sheet over it. Then keep it in place by strapping the elastic band around the top. Once this has been done, simply punch a few holes into the plastic with your knife, making sure that each hole is no larger then the width of a pencil.

http://www.thebugsquad.com/fruit-flies/fruit-fly-trap

That's the source. i just googled it.