ST. LOUIS (AP) — One of every three bites of food we consume depends on pollination by honeybees, but these overlooked contributors to our food system are continuing to die in stubbornly perplexing ways.

Beekeeping groups have held exhaustive conferences. Researchers have organized task forces. The U.S. Department of Agriculture has contributed some of its stretched resources to tracking down the cause of the mysterious deaths, and in a report issued last month, delivered a frustratingly complex answer: Many factors may be responsible, from stress to pesticides.