This photo provided by Taco Bell shows a new advertisement for Doritos Locos Tacos shells. The Mexican-style chain rolls out the Doritos Locos Tacos shells at midnight on Wednesday, March 7, 2012 at its nearly 5,600 restaurants nationwide. The fast-food chain, a unit of Yum Brands Inc., calls it the biggest product launch in its 50-year history. Credit: AP