One of my homies makes light traps attached to sticky cards for flying insects. They're UV LEDs just below spectrum that effects plants- like 390 nanometers I think- and they're equipped with a light sensor so when the grow lights go out the trap lights go on. It's pretty simple and works amazingly well.
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Tested them cautiously until I was satisfied they indeed did not affect flowering plants' photosensitivity in any way. Now I always have a couple in my flowering rooms just as a precaution to alert me immediately if the gnats are present.
I have an ant colony invading my house, and I poisoned them so they're currently in the stage where they send out flyers looking for new place to host a colony. So I set up a uv trap right near the access point- check out these nasty bastards:
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The light traps used in conjunction with gnatrol the gnats don't stand a chance. Never around for more than a week when used together.