"All the bees we've looked at, you can't look at a single cause," said Jeffrey Pettis, research leader for the Department of Agriculture in Beltsville, Md.
Mendes, the Florida beekeeper, says he's concerned. He says he has friends whose bees died off if they were next to cultivated farmland, and he wonders if there's something spreading from them worldwide; there have been bee-population collapses as far away as Europe and India.
"In many ways we view honeybees as an indicator species," like the proverbial canary in the coal mine, he said. "We don't know what's going on. And we all share the same earth."