Spider mites, possibly mealy bugs as well.
I'd give the diatomaceous earth (DE) a go as well. I use a duster like the one pictured below.
I also mix in a bit of powdered sulfur and cinnamon as well foe a bit of fungal protection.
While DE is non-toxic you do need to be cautious with it. I recommend wearing a dust mask to avoid inhaling the dust which can cause respiratory irritation. It will also indiscriminately kill all insects, both harmful and beneficial that come into contact with it (it is made up of microscopic fossils which pierce the outsides of insects and cause them to die).