Stress could be behind the sharp collapse in honeybee colonies

February 12, 2015 2:12 am

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.

Stress could be behind the collapse in bee colonies. Photo / Thinkstock
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.

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.
“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.

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