Make a soda bottle trap:
Remove the lid and label from a clean, empty plastic two-liter soda bottle.
Carefully remove the upper third of the bottle by cutting along its circumference at approximately where the top of the label used to be.
Roll a cone out of a piece of paper to fit inside of the bottle without touching the bottom. Secure with tape.
Make a small (like half a centimeter) hole in the bottom of the cone.
Put an attractive liquid such as orange juice o(or old fruit) in the cup-shaped part of the now-severed bottle.
Turn the cone upside-down (ice cream cone style) and insert it into the cup-shaped bottom part of the bottle. Seal the seam at the top of the bottle with duct tape.
Fruit flies find their way into the bottle, but they can't get back out. After flies are trapped inside, simply seal the bottle in a plastic shopping bag, throw out, and make a new one.
Log on here and it will show you what it should look like:
view linkEvery week or so, empty the container and put in fresh bait.