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ISIS Press Release 11/06/08
To Bee Organic or not to Bee
Prof. Joe Cummins explains
why bees are especially susceptible to pesticides
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Worsening epidemic of Colony Collapse
Colony Collapse Disorder (CCD), a growing scourge of honeybees has
struck again this year. The United Sates Department of Agriculture (USDA)
reported a 36 percent loss of colonies in managed hives over the winter, up
13.5 percent from the previous year [1]. USDA has yet to identify a single
pathogen responsible for the disease, and has finally begun to study the interaction
between pesticides and viruses or varroa mites as possible causes [2].
CCD is characterised by the complete absence of adult
bees in the colonies with little build-up of dead bees in or around the colonies,
but capped brood and food stores of both honey and bee bread are present,
and are not immediately robbed by other bees. Attacks by hive pests such as
wax moth and small hive beetle, if any, are noticeably delayed.
In a colony undergoing collapse, the workforce is insufficient
to maintain the brood, and seems to be made up mostly of young adult bees.
The queen bee is present, but the cluster is reluctant to consume provided
feed such as sugar syrup and protein supplement [3].
The Institute of Science in Society has reviewed the
evidence on the impact of pesticides and the synergistic interaction between
pesticides (including Bt biopesticides now widely incorporated into genetically
modified (GM) crops) and
pathogens such as the fungal parasites [4-6] (Requiem for the Honeybee,
Mystery of Disappearing
Honeybees, SiS 34; Parasitic Fungi and Pesticides
Act Synergistically to Kill Honeybees? SiS 35). That evidence was
the basis for question to the European parliament urging immediate bans on
the pesticides such as the neonicotinoid insecticides as well as GM crops containing Bt biopesticides [7] (Emergency Motion on Protecting the Honeybee,
SiS 35).
In 2008, the German government took the extraordinary step of banning neonicotinoid
pesticides (see Emergency Pesticide Ban for Saving the Honeybee, SiS 39).
Genetics of the honeybee
The honeybee genome has been sequenced, and while rich in genes for
behaviour and learning relative to other insects, it is deficient in genes
for immunity and the ability to detoxify toxic chemicals such as the pesticides
[8]. The genes families involved in insecticide resistance in other insects
are completely lacking. These shortfalls contribute to the sensitivity of
bees to insecticides [9]. Bees have been found to have immune systems comparable
to insects such as flies and mosquitoes, but with about one third less genes
devoted to immunity than other insects. Insects immunity involves inducible
synthesis of anti-microbial peptides and constitutive melanisation-encapsulation
response to pathogens The reduced immune flexibility of the honeybee may
be compensated by social activity such as hive cleaning [10]. When bees are
challenged by a bacterial pathogen, genes in the
head of the bee are differentially expressed, and show neuroimmune-behaviour
interactions similar to those of vertebrates [11]. A dysfunction in both
its immune response and behaviour triggered by exposure to pesticides could
easily result in CCD.
The genetics of honey bees is now actively investigated. The
male honeybee has 24 chromosomes (linkage groups) and mapping of the numerous
genes has been achieved. Males are normally haploid, but diploid males
are observed at low frequency. Worker bees and queens are diploid. One queen
bee provides over 2 000 eggs per day; unfertilized eggs become males while
fertilized eggs become workers [12]. Bee breeding has had some success, but
complicated by the breeding habit of the queen, which copulates while flying
to avoid inbreeding depression. The problem of inbreeding in honeybees has
been studied for over fifty years, and before that, beekeepers have recognized
the problem for centuries. The population genetics of inbreeding and homozygosis
(too many genes existing as identical pairs) was
worked out in 1950 by James Crow and William Roberts in [13]. Heterosis (hybrid
vigour) in the honeybee was described in 1955 by Gladstone Gale Jr. and John
Gower [14]. There has been no evidence that inbreeding contributed
to CCD because the experienced beekeepers recognize the problem and overcome
it by providing for out-breeding. However, it is clear that the toll of CCD
may result in obligatory inbreeding due to shrinkage of the bee population,
and that will accelerate the demise of the honeybee.
To bee organic
Organic farms are proving to be sanctuaries for the honeybee from
the ravages of CCD. The honeybees are exquisite social animals perfectly adapted
for pollination and honey making, but far too delicate to withstand the onslaught
of systemic pesticides and GM crops. Regulators are slow to control the environmental
insults to the honeybees and unprepared to act on the precautionary principle.
Saving the honeybee may be among the most compelling reasons to shift comprehensively
to organic agriculture [15] (Saving the Honeybee
Through Organic Farming, SiS 38).
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