The bee varroa and tracheal mites were an issue several years ago, and a lot of colonies were lost. But this new threat is much more devastating, and no biological cause has been officially confirmed. The workers leave the colony and don't come back, which ensures that the colony will die. I've heard reports that even wax moths won't infest the comb in CCD-affected hives, which may indicate that a toxin is in there that repels or kills wax moths.

Ladybugs cannot eat the mites that exist in the throats of bees...it would be a tight fit.