If they are doing no damage to your plants is it possible that they are a beneficial insect. And could be keeping something else at bay? They must be eating something, especially since they are getting more prolific. I made the mistake of using a systemic poison last season and when it wore off my plants were decimated by broad mites. And they suck quite a lot, lesson learned. Sinking is worth a go, looks like they are up under the lip of the pot as well eh. Good luck.