I'm 100% coco and have had this problem. I used yellow glue boards, like a lot of them. Also, switched to watering from the bottom at the drip tray. No rain, no hatch! Also, adding course gravel on top of the medium will make them hate life. They shouldn't be able to fly/crawl up through it. I've heard that neem oil is a fix, but have no experience with it since my glue boards and other fixes have kept this problem in check.