Part of the reason was weather related, but part may be attributed to the occurence of two new mites, varroa and tracheal, which transmit viral infections among bees, and which have a detrimental effect of their own. Commercial bee farms are actually expanding their operations, and the number of hives available for pollination will probably be greater next year than it was last year. However, in areas where gardens are entirely dependent on wild pollinators, crops may be down a bit. It is expected that some of the wild bees are resistant to the mites and the viruses which they transmit and they will eventually repopulate the feral, or wild, colonies. This may take a few seasons.
Chemicals are commercially available to reduce the number of mites in a hive.
They are not too expensive to purchase and apply. You wanted information on tracheal mites. The problem need not destroy your hives. There are several options available to beekeepers to treat hives which may have this pest. Menthol treatments are legal, approved chemical treatments for tracheal mites.