We had a vacant block beside our old house with clay soil and a hollow in it. Water would hang around for weeks. The council said there were no mozzies in it but they weren't interested in the flies.
We used these traps and they would nearly fill up. How many dead flies per litre? I think in the end though we actually broke the cycle and reduced the number significantly. That was a worthwhile achievement. Screens, plants and an occasional spray won't achieve this.
