Honeybees around the world are struggling to cope with colony collapse disorder, a mysterious malady that can turn a seemingly healthy hive into a ghost town. While the decade-old plague seems to have a variety of causes — including pesticides, parasites and habitat loss — new research reveals a "major factor" that can speed up a colony's downfall: baby bees growing up too quickly.
Under normal conditions, a young honeybee begins foraging when she's about 2 or 3 weeks old. If disease, food shortages or other factors kill off too many older bees in her colony, she might start foraging at an earlier age to help pick up the slack. Known as "precocious foraging," this is an adaptive response that can help a hive endure fleeting periods of misfortune. According to the newly published study, however, it can backfire in the face of a chronic hardship like colony collapse disorder.
"Young bees leaving the hive early is likely to be an adaptive behaviour to a reduction in the number of older foraging bees," says lead author Clint Perry, a research fellow at Queen Mary University of London, in a statement about the new study. "But if the increased death rate continues for too long or the hive isn't big enough to withstand it in the short term, this natural response could upset the societal balance of the colony and have catastrophic consequences."
To test how younger foragers affect the health of a colony, the researchers set up experimental hives populated only with young bees, à la "Lord of the Flies." They also kept tabs on bees in a healthy hive, where pheromones help preserve traditional social roles. By attaching tiny radio trackers to thousands of these bees, the researchers could then follow each insect throughout her life.
They found that bees who started foraging at a younger age completed fewer foraging flights than other bees and were more likely to not survive their first flights. That might be worth the tradeoff at first, but over time it can create a feedback loop that "dramatically" accelerates population decline.
The researchers then entered this data into a computer model that simulates a hive. The results suggest the use of younger foragers is more of a stopgap strategy — if mortality rises too high or adult populations stay low for too long, the colony can reach a tipping point. More and more bees begin foraging at younger ages, the study found, resulting in less food storage and fewer newborn bees.
"This compounds the stresses on the colony and accelerates failure," the researchers write.
Colony collapse disorder (CCD) isn't just bad news for bees. It has major implications for global agriculture, since bees provide crucial pollination for a wide range of food crops, including almonds, apples, cucumbers, carrots and many others. In the U.S. alone, bees pollinate an estimated $15 billion worth of crops every year. This is what a typical grocery store might look like without bees.
Confusion about the causes of CCD makes the phenomenon especially difficult to combat. While varroa mites and viruses play an important role in wiping out many hives, research also points to the widespread use of pesticides on the plants bees pollinate, namely a class of insecticides known as neonicotinoids. The abruptness of CCD often catches beekeepers by surprise, so anything that can enable an earlier diagnosis — such as the ages of foragers — might provide a boost.
"Our results suggest that tracking when bees begin to forage may be a good indicator of the overall health of a hive," Perry says. "Our work sheds light on the reasons behind colony collapse and could help in the search for ways of preventing colony collapse."
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