Aha, I have same problem. It is the only pot survived from snow storm last winter. I cut the stems infected, picked and killed the bugs with bamboo skewer, then re-planted them in a new pot.

The plants in the first pot are doing great. They are healhty and have many new tips. The second pot with cleaned stems are ok eventhough still have the white stuff.

Good luck.

Imidacloprid is a systemic soil drench that will eradicate mealies. They are difficult to control with alcohol and horticultural oils. Prevention is the key, but is difficult to quantify.