Report # 1 on yellow sticky traps! I order a set (5) each of blue and yellow, and they came in a few days ago. I opened one yellow. You turn it to have the sticky sides out, duh, and the edge/top isn't sticky. Hole on top side. I rigged with a baggie tie and string to hang over the seed starts, about 6 small 10 pellet trays. I didn't think I had many fungus gnats, but in 3 days near 20 are stuck. (I've only seen a couple on the dirt!) I will put up more when the basil pots come in, and also have more of the nursery/childcare inside. Next season will work with more in the nursery outside to get whatever is getting the plants.
I would think they'd be great in indoor starting areas and greenhouses.