Them are them damn root aphids, and they will start migrating up the stalks into the plants so you need to smear the stalks with tanglefoot, it is a nasty sticky mess like vasiline mixed with contact cement. you can also use double sided sticky tape.
There needs to be at least 2-3 inches of the stalk covered. this will catch the ones that are on the move, also a stripe around the container near the bottom.thats for containment,also if there are lots this sticky stuff will need replaced
Now the treatment, Pyrethem spray kills them

Daddy