Colony Collapse Disorder (CCD) is a significant threat to honey bee populations worldwide. The decline in honey production is a relatively minor issue compared to the loss of pollinators for vital crop production.

The problem is that, while many descriptions of the disorder are available the cause of the problem remains unknown. Pesticides, pathogens, parasites, environmental problems an poor management are all being investigated as possible causes according to the US Department of Agriculture (USDA).

In the United States, “colony losses from CCD are a very serious problem for beekeepers. Annual losses from the winter of 2006-2011 averaged about 33 percent each year, with a third of these losses attributed to CCD by beekeepers. The winter of 2011-2012 was an exception, when total losses dropped to 22 percent,” according to the USDA website.

Now researchers at Queen Mary University of London (QMUL), Macquarie University in Sydney, Washington University in St Louis, and University of Sydney. While their study doesn’t nail down a specific environmental cause, it does describe how and why colonies collapse.

According to the scientists involved, Bees normally begin foraging when they are 2-3 weeks old. However, when colonies become distressed by factors that kill older bees, the young bees begin foraging at an earlier age.

For the purpose of the study, thousands of radio trackers were attached to bees and the animals were tracked over the course of their lives. The researchers found that the younger bees were when they began foraging, the less successful they were at foraging and the more likely they were to die on their first flights.

Any stress that lead to chronic forager death among the older bees, led to a younger work force, less success at foraging and accelerated death among foragers. This spiral led to an accelerated decline of the colony of the type described as CCD.

“Young bees leaving the hive early is likely to be an adaptive behaviour to a reduction in the number of older foraging bees. 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,” said Dr Clint Perry from the School of Biological and Chemical Sciences at QMUL, in a statement.

“Our results suggest that tracking when bees begin to forage may be a good indicator of the overall health of a hive. Our work sheds light on the reasons behind colony collapse and could help in the search for ways of preventing colony collapse,” he added.

The researchers do not mention which specific stresses lead to the death of the older bees to begin the process. However the research does shed light on the process that leads to the loss of an entire colony, rather than the death of individual bees.

California beekeeper Randy Oliver told the Los Angeles Times that the research, published in the Proceedings of the National Academy of Sciences, fits with what he has observed in the field.

“What we observe in the field is the sign of a poor bee-to-brood ratio, an indicator that adult bees are dying more rapidly than the colony can replace them. Sudden collapse may soon follow,” said Oliver.