It seems like magnification time!
We want to see some cool mite pics!
I keep a few eye loupes and lenses around for things like this, and they are invaluable!
Also good for removing splinters in my fingers!
That should help you decide what to do next, for if you see them, it explains everything, including their eminent destruction!
If you find none, then you alone must still decide! Do nothing and wait.... , look for other causes, or spray the plant "just in case". Ah, look at all the experience you are getting thru this! Looking at plants and things "up close" is not to be missed either! I would suggest getting a close-up lens of sorts anyway, if you don't already have one.
Why would they only be on this plant? Easy question! (I have had one plant colonized in my greenhouse, while nearby plants were totally unaffected!) And why...? Well, taste of course!
In fact, I had a certain garden poppy in my yard years ago, that the aphids loved! But only this one variety! (It was an annual "drug" type poppy that used to be commonly sold because it had really nice flowers, before everyone worried that growing these would turn everyone into addicts!) Anyway, all the aphids would turn black from the resin and THEY were the ones who apparently got addicted to it! Wouldn't touch another plant, but were all over these! So yea, my vote is "taste", right after "they like it 'cause it makes them high"!
And it seems Bayer Advanced has "improved" their product with imidacloprid , as it now kills bugs and then makes you need to buy more!