[ExI] Studies show how pesticides make bees lose their way

[Eugen Leitl]

http://uk.reuters.com/article/2012/03/29/us-science-pesticides-bees-idUKBRE82S12P20120329

Studies show how pesticides make bees lose their way

A bee is seen sitting on a Marigold flower in a field of a private plantation
near the village of Pishchalovo, about 220 km (138 miles) east of Minsk in
this July 18, 2011 file photogaph. REUTERS/Vasily Fedosenko/Files

By Kate Kelland

LONDON | Thu Mar 29, 2012 7:42pm BST

(Reuters) - Scientists have discovered ways in which even low doses of widely
used pesticides can harm bumblebees and honeybees, interfering with their
homing abilities and making them lose their way.

In two studies published in the journal Science on Thursday, British and
French researchers looked at bees and neonicotinoid insecticides - a class
introduced in the 1990s now among the most commonly used crop pesticides in
the world.

In recent years, bee populations have been dropping rapidly, partly due to a
phenomenon known as Colony Collapse Disorder. Scientists also fear pesticides
are destroying bee populations, but it is not clear how they are causing
damage.

Dave Goulson of Stirling University in Scotland, who led the British study,
said some bumblebee species have declined hugely.

"In North America, several bumblebee species which used to be common have
more or less disappeared from the entire continent," while in Britain, three
species have become extinct, he said in a statement.

The threat to bee populations also extends to Asia, South America and the
Middle East, experts say.

Bees are important pollinators of flowering plants, including many fruit and
vegetable crops. A 2011 United Nations report estimated that bees and other
pollinators such as butterflies, beetles or birds do work worth 153 billion
euros ($203 billion) a year to the human economy.

In the first of the Science studies, a University of Stirling team exposed
developing colonies of bumblebees to low levels of a neonicotinoid called
imidacloprid, and then placed the colonies in an enclosed field site where
the bees could fly around collecting pollen under natural conditions for six
weeks.

At the beginning and end of the experiment, the researchers weighed each of
the bumblebee nests - which included the bees, wax, honey, bee grubs and
pollen - to see how much the colony had grown.

Compared to control colonies not exposed to imidacloprid, the researchers
found the treated colonies gained less weight, suggesting less food was
coming in.

The treated colonies were on average eight to 12 percent smaller than the
control colonies at the end of the experiment, and also produced about 85
percent fewer queens - a finding that is key because queens produce the next
generation of bees.

In the separate study, a team led by Mickael Henry of the French National
Institute for Agricultural Research (INRA) in Avignon tagged free-ranging
honeybees with tiny radio-frequency identification microchips glued to each
bee's back. This allowed them to track the bees as they came and went from
hives.

The researchers gave some of the bees a low dose of the neonicotinoid
pesticide thiamethoxam which they knew would not kill them and compared them
to a control group of bees that was not exposed to the pesticide.

The treated bees were about two to three times more likely to die while away
from their nests, and the researchers said this was probably because the
pesticide interfered with the bees' homing systems, so they couldn't find
their way home.

Henry said the findings raised important issues about pesticide authorization
procedures.

"So far, they (the procedures) mostly require manufacturers to ensure that
doses encountered on the field do not kill bees, but they basically ignore
the consequences of doses that do not kill them but may cause behavioral
difficulties," he said in a statement.

($1 = 0.7525 euros)

(Reporting by Kate Kelland; Editing by Karolina Tagaris)