Scientists are at a loss to pinpoint the cause. The die-off in 35 states has crippled beekeepers and threatened many crops.

The dead bees under Dennis vanEngelsdorp's microscope were like none he had ever seen

He had expected to see mites or amoebas, perennial pests of bees. Instead, he found internal organs swollen with debris and strangely blackened. The bees' intestinal tracts were scarred, and their rectums were abnormally full of what appeared to be partly digested pollen. Dark marks on the sting glands were telltale signs of infection

Scientists have scoured the country, finding eerily abandoned hives in which the bees seem to have simply left their honey and broods of baby bees

The scene is being repeated throughout the country, where honeybees, scientifically known as Apis mellifera, are required to pollinate a third of the nation's food crops, including almonds, cherries, blueberries, pears, strawberries and pumpkins