I've made fruit fly traps placing either wine or balsamic vinegar inside a jar with a few drops of dishwashing liquid added. I put a top with either a piece of paper fashioned into a cone taped to the top without any escape spots. The fruit flies enter through the tiny hole that's the bottom of the funnel, but they can't escape and therefore drown. I've also taken a shallow dish with the liquids added, place a piece of saran wrap tightly over the top, poke some little holes into the saran, and set the traps close to the most heavily populated areas.