Something is killing the nation's honeybees. Dave Hackenberg of central Pennsylvania had 3,000 hives and figures he has lost all but about 800 of them. In labs at Pennsylvania State University, the Pennsylvania Department of Agriculture, and elsewhere in the nation, researchers have been stunned by the number of calls about the mysterious losses. "Every day, you hear of another operator," said Dennis vanEngelsdorp, acting state apiarist with the Pennsylvania Department of Agriculture. "It's just causing so much death so quickly that it's startling." At stake is the work the honeybees do, pollinating more than $15 billion worth of U.S....