if you've seen flyers and you're describing the quantity as 10-20 per sq inch, to me sounds like root aphids..... thats how the cycle goes. when populations reach a certain "critical" level, all of a sudden flyers emerge. The flyers are the easiest to kill. even if you put 1 mL of neem in a liter of water and spray all the foliage you'll kill em on contact. Once you verify that they are aphids.....you'll have a lot of work ahead of you. So start planning just in case......
BM
BM