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ISIS Report 24/04/07
Requiem for the Honeybee
Neonicotinoid insecticides used both in sprays and seed dressing may be
responsible for the collapse of honeybee colonies. Prof.
Joe Cummins
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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 [1] (The
Mystery of Disappearing Honeybees, this series). The United States National Research Council
(USNRC) Committee of the Status of Pollinators in North America report [2] 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 on that account.
On the other hand, any suggestion that GM crops and pesticides may be causing
the decline of honeybees is met with heated denial from the proponents.
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 [3]. 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 [4]. Analysis of maize and sunflower crops originating from
seeds dressed with imidacloprid indicated that large amounts of the insecticide
will be carried back to honey bee colonies [5]. 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 [6].
Imidacloprid in sucrose solution
fed to the bees in the laboratory impaired their communication for a few hours [7]. Sub-lethal doses of imidacloprid
in laboratory and field experiment decreased flight activity and olfactory discrimination, and olfactory
learning performance was impaired [8].
Bayer corporation
scientists reported that neither honeybees exposed to imidacloprid in sunflower
seeds dressed with the insecticide [9] nor maize seeds dressed with the insecticide
or released from the seeds during planting [10] 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 [11]. 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 [12], without, however, disproving the findings.
It is simply yet another case of the anti-precaution principle
being applied [13] (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 [14], and is more like a death camp for insects.
Monsanto’s US Patent 6,660,690 provides for coating GM seeds with chemical
pesticides [15].
Toxicology known
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 [16]. 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 bees [17].
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
become extinct.
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