(Update 1: adds MBIA comments) Call it the bond insurer crisis, part two: Fitch Ratings on Friday said it had downgraded a core rating of industry giant MBIA Inc. [stock MBI][/stock] and its subsidiaries amid concerns over capital adequacy. The rating agency moved MBIA’s core insurer financial strength rating to AA, from it’s previous perch at the AAA level, the latest in a series of downgrades to beset the bond insurance industry.