I don't know what I'm up against and I'm pretty panicked because my favorite tree is at risk. I repotted my river birch at the end of March so it was already pretty weak when it was targeted by some unknown adversary. As soon as the leaves started emerging I noticed that they were coated with some whitish powdery substance that I thought was powdery mildewy. After that all the leaves started drooping and I noticed that the powdery white substance had bugs crawling through it. To me they don't look like scale and they don't look like mites and they don't look like aphids. Before I used a magnifying loop, I thought that they might be mealybugs, so I treated the tree with imidacloprid on Saturday. I don't know what the uptake time is but it doesn't appear to have done it's work because I swear more of the leaves are coated in bugs. I broke out the magnification and took some pictures, and I would truly appreciate some help identifying my adversary, and if you could spare some advice on a strategy moving forward, I would be deeply grateful. The pictures are kind of gory, as a warning.