Spreads from mites hanging on to hair tips attack points-to go from older bees to younger bees. Varroa mites - spreads disease like tracheal,but size is huge by comparison. Can see on bee or especially on brood. As big as a volleyball size tick on you. Both varroa and tracheal were noticed in USA about 1986-1988 and have spread to all the USA since then.
Females feed on developing and emerged bees.
Nosema - Spores are ingested by adult bee and germinate in mid gut by way of a tube which penetrates the gut wall and the spores travel into the gut cells. Chaulkbrood - first sign is small peroration in cappings. Open up and there will be pupa covered with white stuff. Natures way of cleaning up dead and dying hives. Fall- as soon as last super is off,preferably in August.