Two new studies have pinned the blame for the catastrophic decline in bee numbers on a commonly-used class of pesticides.
Neonicotinoids are the best-selling insecticides in the world, with global sales of over $1 billion. They are broadly used on many flowering crops, such as oilseed rape and sunflowers, as a seed dressing to protect them against pests. However, the chemicals then travel right through the plant, and low levels are found in the nectar and pollen.
While they're controlled in Germany, Italy and France, they're still widely used in the US and elsewhere.
A study from the University of Stirling in Scotland now shows that bumblebee nests that were exposed to such low levels for just two weeks subsequently grew more slowly. They also showed an 85 percent reduction in the number of new queens they produced.
"Our work suggests that trace exposure of our wild bees to insecticides is having a major impact on their populations," says professor Dave Goulson.
"Only queen bumblebees survive the winter to build new nests in the spring, so reducing the number produced by 85 percent means far fewer nests the following year. Repeated year on year, the long term cumulative effects are likely to be profound."
Meanwhile, scientists at France's National Institute for Agricultural Research (INRA) attached RFID tags to honeybees, and exposed them to a dose of the neonicotinoid thiamethoxam.
The bees became disoriented, and were unable to find their way home.
"There is a clear need to re-evaluate the safety of these chemicals," says Goulson.
Neonicotinoids probably aren't the only problem bees are facing. Previous studies have suggested that so-called colony collapse could also be linked to viruses, mites and climate change - even, controversially, to cellphone use.