I don't think that the imidacloprid is going to do much at all. It's an insecticide, not a miticide- very differant beasties.

The methiocarb is active against mites, but it's contact only with a long and scary residual- application will have to be very thourough. Please be careful with this stuff- it's sorta nasty.

I've had fairly good results against mites using spinosyn a/d compounds- and excellant results using abamectin. Abamectin would be my chemistry of choice.

The miticide specific product is called Avid- it's a mainstay of the commercial floriculture industry. It's relatively safe- same coumpound used in flea and tick collars for pets. You've probabley already handled some.

Check and see if the products that you're using are registered as miticides- mites aren't insects, and only a few insecticides will control them, and then only incidentally.