Scientific American By Francie Diep 10/10/13
Scientists are gaining a more sophisticated understanding of the role of toxins in worldwide bee declines as lab studies of single insects are superseded by research on hives in the field
A honeybee's brain is hardly bigger than the tip of a dog's whisker, yet you can train a bee just as Pavlov got his pups to drool on hearing their dinner bell. Using a sugar solution as a reward, you can teach the insect to extend its little mouthparts in response to different scents.
Several Pavlovian lab studies of individual worker honeybees, however, found that those fed small amounts of pesticides—especially a class called neonicotinoids—do not learn which scents lead to a sweet reward as quickly as their pesticide-free peers do. Yet, until recently, it wasn't clear what these and other lab studies meant for the health of entire bee colonies, which might have strategies to mitigate the overall impact of problems with particular hive members. "Just because you see the effect in the bee in the lab, strapped into this lab apparatus, [doesn’t mean you know] how does this translate into a colony in a field?" says Reed Johnson, an entomologist at The Ohio State University who studies pesticides' effects on honeybees.
To probe the colony question, academic research on neonicotinoids and other pesticides is moving from studies in labs to the outdoors—examining both the effects on entire honeybee or bumblebee hives as well as those on solitary bees nesting near crops. Such studies could help determine how and to what extent pesticides are behind the accelerated rate at which honeybee hives are dying. They also seek to answer whether pesticides are harming other bee species that are important to agriculture.
Since 2006 U.S. honeybee-keepers have reported they lose 30 percent of their hiveson average after every winter. Before then, beekeepers would usually lose 5 or 10 percent of their hives after winter. The immediate reasons keepers report their hives are dying seem ordinary enough—winter starvation, pests such as the varroa mite and problems with queen bees such as premature deaths—but researchers are trying to understand why these seemingly normal problems are now happening at an extraordinarily higher rate. Pesticides could be one answer.
So far, honeybee-keepers have replaced lost hives through breeding, but experts worry that in the future bees won't be able to sustain such a high replacement rate. Populations could decline below what U.S. agriculture needs to pollinate America's nuts, fruits, vegetables and even livestock feed.
What do we know?
The field studies entomologists repeatedly cite include ones that found different neonicotinoids reduced the number of honeybee foragers that return to their hive as well as reduced the population growth and queen bee production of bumblebee colonies. Another study found that the neonicotinoid imidacloprid, when applied in combination with another popular, non-neonicotinoid pesticide called lambda-cyhalothrin, increased the likelihood that bumblebee hives will fail. "I do think it is pretty clear that neonics interfere with bees' ability to forage effectively," says David Goulson, a bumblebee researcher with the University of Sussex in the U.K. and an author of the bumblebee population growth study cited above. "For bumblebees, the evidence is overwhelming."