Wholesale prices skyrocketed at an annual rate of 12.7 percent in January, the biggest monthly surge in more than three years, the government said Friday. The Labor Department said the steepest increase in food prices in a year combined with the largest rise in energy prices in two years to push up the Producer Price Index 1.0 percent last month. It was the biggest increase since an identical surge in October 1985. The index hasn't risen faster in a single month since April 1981, when it shot up 1.1 percent. The large gain surprised analysts, who were expecting a moderate 0.3 percent to 0.4 percent increase.