The DE cuts the bugs bodies up, when they climb through it. It works best if you water from the bottom, as pcduck said don't water in....once it's wet, it doesn't work. Most use the food grade version, can get on Amazon or local home center.
Depending on what kind of bugs you have. I would get SNS 217 to get rid of them, and SNS 209 to keep them away. Go to Sierra Natural Science website. They have free trial kits. You just have to pay for shipping. If they're mites. You don't want to **** around. It could turn very bad very quickly if untreated. SNS is the only way to go in my opinion