Monsanto is hosting a "Bee Summit." Bayer AG is breaking ground on a "Bee Care Center." And Sygenta AG is funding grants for research into the accelerating demise of honeybees in the United States, where the insects pollinate fruits and vegetables that make up roughly a quarter of the American diet. The agrichemical companies are taking these initiatives at a time when their best-selling pesticides are under fire from environmental and food activists who say the chemicals are killing off millions of bees. .. Die-offs of bee populations have accelerated over the last few years to a rate the U.S....