Beekeepers have seen hive after hive fall prey to colony collapse disorder (CCD). Now insights from the honeybee genome could overthrow guesswork in the effort to diagnose the cause of the die-offs.

May Berenbaum at the University of Illinois, Urbana-Champaign, and her colleagues looked for genetic differences between bees from US colonies that have suffered CCD and bees that were sampled before colony collapses shot up in 2006. CCD killed off about a third of US honeybees in 2007 and 2008.

The team found 65 genes that were distinctly different in CCD bees. They also discovered unusual snippets of genetic material that are typical of infection with the RNA viruses known as picorna-like viruses. They found no evidence to suggest that pesticides or bacterial infection are the primary cause of CCD. Berenbaum thinks picorna-like viruses may be the root cause, making the bees highly vulnerable to other viruses, pesticides and bacteria.