24 April 2007
Requiem for the Honeybee
Neoniccotinoid insecticides used in seed dressing may be responsible for
the collapse of honeybee colonies
Prof. Joe Cummins
Neonicotinoid insecticides are harmful to the honeybee
There has been a great deal of concern over the decline of the honeybee
across the US, Europe and Australia  (The Mystery of Disappearing
Honeybees, this series). The United States National Research Council
(USNRC) Committee of the Status of Pollinators in North America report
 focused on the impact of parasites, fungi, bacteria and viruses, but
did not pay much attention on the impact of pesticides and genetically
modified (GM) crops, which may have lethal or sub-lethal effects on the
bee?s behaviour or resistance to infection. There have been strong
responses to the report. Any suggestion that GM crops and pesticides may
be causing the decline of honeybees is met with heated denial from the
Certainly, honeybees are declining both in areas where GM crops are
widely grown, and in other areas where GM crops are released in small
test plots. Is there a common thread that links both areas? Yes there
is, the universal use of systemic pesticide seed dressing in GM crops
and conventional crops; in particular, the widespread application of a
relatively new class of systemic insecticides - the neonicotinoids -
that are highly toxic to insects including bees at very low
concentrations. Systemic pesticide seed dressings protect the newly
sprouted seed at a vulnerable time in the plant?s development. Seed
dressings include systemic insecticides and fungicides, which often act
synergistically in controlling early seedling pests.
The neonicotinoid insecticides include imidacloprid, thiamethoxam,
clothianidin, and several others. Imidacloprid is used extensively in
seed dressing for field and horticultural crops, and particularly for
maize, sunflower and rapeseed (canola). Imidacloprid was detected in
soils, plant tissues and pollen using HPLC coupled to a mass
spectrometer. The levels of the insecticide found in pollen suggested
probable delirious effects on honeybees . For several years since
2000, French and Italian beekeepers have been noticing that imidacloprid
is lethal to bees, and the insecticide is suspected to be causing the
decline of hive populations by affecting the bee?s orientation and
ability to return to the hive.
Confused and disoriented bees
A team of scientist led by the National Institute of Beekeeping in
Bologna, Italy, found that pollen obtained from seeds dressed with
imidacloprid contains significant levels of the insesticide, and
suggested that the polluted pollen was one of the main causes of
honeybee colony collapse . Analysis of maize and sunflower crops
originating from seeds dressed with imidacloprid suggest that large
amounts of the insecticide will be carried back to honey bee colonies
. Sub-lethal doses of imidacloprid in sucrose solution affected
homing and foraging activity of honeybees. Bees fed with 500 or 1 000
ppb (parts per billion) of the insecticide in sucrose solutions failed
to return to the hive and disappeared altogether, while bees that had
imbibed 100 ppb solutions were delayed for 24 h compared with controls.
. Imidacloprid in sucrose solution fed to the bees in the laboratory
impaired their communication for a few hours . Sub-lethal doses of
imidacloprid in laboratory and field experiment decreased flight
activity and olfactory discrimination, and olfactory learning
performance was impaired ..
Bayer corporation scientists reported that neither honeybees exposed to
imidacloprid in sunflower seeds dressed with the insecticide  nor
maize seeds dressed with the insecticide or released from the seeds
during planting  were detrimental to honeybees. The Bayer studies
did not deal with sub-lethal behaviour of intoxicated bees. An
independent study found that imidacloprid was released to the
environment from treated maize seeds during seed planting . Bayer
eco-toxicologists directed harsh criticisms at reports showing lethal or
sub-lethal toxic effects of imidicloprid seed dressing and concluded
that imidacloprid does not pose any significant risk to honeybees in the
field , without, however, disproving the findings. It is simply yet
another case of the anti-precaution principle being applied  (Use
and Abuse of the Precautionary Principle, ISIS News 6)
Turning to GM crops such as maize, canola, cotton and soybean it is
clear that all of these GM crops, with or without Bt genes, use seeds
most of which are coated with neonicotinoid pesticides highly toxic to
honey bees. For example, Herculex maize with Bt genes to control
rootworm, like Yieldgard corn borer resistant maize, is planted with
seeds dressed with a neonicotinoid insecticide and a fungicide.
Furthermore, the GM planting requires setting aside plots of non-GM
maize making up 20 percent of the planted area as a ?refuge? to
discourage the evolution of resistant insects. But the ?refuge? is
sprayed with neonicotinoid pesticide to protect its yield , and is
more like a death camp for insects. Monsanto?s US Patent 6,660,690
provides for coating GM seeds with chemical pesticides .
The toxicology of neonicotinoid insecticides is well known. The
insecticides are inhibitors of acetycholine receptors (i.e., they are
nerve poisons). They have low toxicity for mammals, birds and fish, and
are used to control fleas on dogs and cats . The nicotinic
acetylcholine receptor gene family of the honeybee has been studied; it
has 11 subunit members, a larger number than the fruit fly or mosquito.
The genes for the subunits employ alternatively spliced transcripts to
increase receptor diversity, and the messenger RNAs are edited to
replace specific A bases with I bases. Information on the receptor
should allow for development of insecticides that are not harmful to
In conclusion, the US NRC Committee did not deal with the heated debate
over neonicotinoid pesticides and honeybee decline. Instead, that it
seemed to suffer from tunnel vision and to be overcautious about matters
that threaten large corporations.
We urgently need a thoroughly independent committee to consider the full
range of factors that may be contributing to the decline of bees,
including pesticides, GM crops and electronic devices, before the bees
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"You know, you never can tell with bees". Winnie The Pooh http://www