Researchers from the University of Padua in Italy writing in the journal Environmental Science & Technology say the springtime die-offs have been linked to technology used to plant corn coated with insecticides.
In some parts of Europe where farmers use the technology to plant seeds coated with so-called neonicotinoid insecticides, widespread deaths of honeybees have been reported since the introduction of the technique in the late 1990s, they said.
Such insecticides are among the most widely used in the world, popular because they kill insects by paralyzing nerves but have lower toxicity for other animals.
Scientists said they suspected the bee die-offs might be due to particles of the insecticide made airborne by the pneumatic drilling machines used for planting that forcefully suck seeds in and expel a burst of air containing high concentrations of particles of the insecticide coating.
They found that honeybees that flew through the emission cloud of the seeding machines used in mid-March to May corn planting were dying.
Future work on the problem should focus on a way to prevent the seeds from fragmenting inside the pneumatic drilling machines, the researchers said.