I use fly traps and my fly problems are under control.

I think I'm cleaning out the whole neighborhood, since there are sooooo many caught. Wish I had a mosquito trap. There are such things,,,, but they are quite pricey.

I do have an electric zapper inside garage. Overnight, it is the only light on inside garage, so it cleans out the garage of them sqeetos well.

In regards to dust baths, it seems that what we think chickens should use, is in reality different than what chickens choose. I have a section of sand in the run area. Chickens still prefer the dry soil instead. They also do jump into some of my large flower pots in the springtime before they are planted. Pots have a mixture of potting soil, and peat-moss.