How to get rid of gnats ?

Every year around this time, we get invaded by outdoor gnats. They are small enough to get through the screens. Their season starts around end of May through August. The locusts come & rid us of some of them, but there are so many, (gnats) they just have to die off at the end of their season.My husband had tried all kinds of spray, plus we've had pest control here and nothing seems to get rid of these creatures. We live in the country (in the south) amongst lots of trees, so that may have something to do with these creatures. They don't bite. Just a big nuisance. Any ideas on how to eliminate them?

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