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.
UK wildlife winners and losers
UK wildlife winners and losers
Slugs: they thrive in warm, damp conditions and had a great winter
Mediterranean birds: with spring coming early, a number of birds associated with the Med made rare appearances over the summer, including glossy ibises (pictured) and bee-eaters
Mediterranean birds: with spring coming early, a number of birds associated with the Med made rare appearances over the summer, including glossy ibises and bee-eaters (pictured)
Biting insects: the warm summer across Europe drove an influx of butterflies, moths, dragonflies, hoverflies and ladybirds to the UK. This is because the increased competition for food in warmer parts of the continent forced the insects to disperse in search of new supplies, while the rising temperatures made areas in the UK hospitable that would normally be too cold
Trees: thousands of trees around the country were damaged and uprooted as gales buffeted the UK last winter
Seals: some 35 seals have been found dead on the beaches of Cornwall in the past two months, almost twice the normal rate. Although the bad weather is thought to have played a part, the extent of the death toll remains a mystery
Fungi: had a bad year on account of the dry September and the slugs, who were out in force as a result of October’s rain
“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.
“Our work sheds light on the reasons behind colony collapse and could help in the search for ways of preventing colony collapse,” he said.