The sharp decline in honeybees has been linked with a change in the foraging behaviour of young bees brought on by some kind of environmental stress such as parasitic attacks or pesticides, a study has found.

When honeybees are under stress they respond by sending out the youngest and most inexperienced worker bees to forage for food, and these bees are more likely to die prematurely than older workers that started to forage later in life, scientists said.

The cause of colony collapse disorder is still largely unknown, and many scientists believe it is the result of several factors interacting with one another, including exposure to agricultural pesticides and attacks by bee parasites.

Beekeepers protest in 2013

Researchers found the suddenness of a colony’s collapse appears to be related to a change in foraging behaviour whereby younger workers leave the hive in search of food rather than gaining more experience in the safety of the nest, scientists said.

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“Young bees leaving the hive early is likely to be an adaptive behaviour to a reduction in the number of older foraging bees,” said Clint Perry of Queen Mary University of London, the lead author of a 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,” Dr Perry said.

The study, published in the Proceedings of the National Academy of Sciences, used tiny radio tags attached to honeybees of different ages to allow the scientists to monitor their foraging movements to and from the hive.

“Precocious foragers completed far fewer foraging trips in their life, and had a higher risk of death in their first flights,” according to the researchers.

A mathematical model found that as more workers started foraging at an earlier age, the effect had a positive feedback, with the change in behaviour causing more and more young workers to leave the hive, the researchers said.

“This resulted in a breakdown in division of labour and loss of the adult population, leaving only brood, food and a few adults in the hive,” they said.

Colony collapse disorder has caused a 30 per cent average annual loss of honeybees in North America alone over the last decade. A key feature of the disorder is the complete disappearance of worker bees, leaving the hive largely empty of adult bees.

“Our results suggest that tracking when bees begin to forage may be a good indicate of the overall health of a hive,” Dr Perry said.