Are you aware that Bougainvillea isn't hardy for you? It's a more tropical plant.

I'd start by putting it in the kitchen sink and blasting the stems and leaves with the sprayer. Cover the soil so the aphids aren't knocked down into the soil and the roots aren't flooded. Do this several times over the next week or so, and IME that may well take care of it. I've also used garlic spray on aphids, just crushed garlic in water, let sit for a while and then filtered (a coffee filter works well) and sprayed on the plant.

NHB - Yes I'm aware, thank you.

I also grow Adenium, Plumeria, and numerous other tropicals, most of which are in the form of Bonsai. I have plenty of supplemental lighting to keep the Bougie in a vegetative state of growth over the Winter if that's a plausible option.

At this point however, I'm not sure if Bougainvilleas are of the type that have a period of "Obligate Dormancy", or if they can remain healthy and vigorous; growing year around.

Last night I gave it a thorough spray down w/ just water, and that seemed to do the trick. If I see anything tomorrow, I'll use 2/3 strength "Safer Soap" because Wednesday's low is going to be 35*.

Thanks again,

Rob