The decline of honeybees seen in many countries may be caused by reduced plant diversity, research suggests.
Bees fed pollen from a range of plants showed signs of having a healthier immune system than those eating pollen from a single type, scientists found.
Writing in the journal Biology Letters, the French team says that bees need a fully functional immune system in order to sterilise food for the colony.
Other research has shown that bees and wild flowers are declining in step.
Two years ago, scientists in the UK and The Netherlands reported that the diversity of bees and other insects was falling alongside the diversity of plants they fed on and pollinated.