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Synergistic effects of pesticides and parasitic fungi and worsening decline
The decline of the honeybee attracted
worldwide attention in 2007. Investigations carried out by the Institute of
Science in Society implicated a synergistic interaction between the recent widespread use of new pesticides
(including Bt toxin from GM crops) and fungal infections [1, 2] (Parasitic Fungus and Honeybee Decline
, Parasitic Fungi
and Pesticides Act Synergistically to Kill Honeybees?, SiS 35). Sub-lethal levels of neonicotinoid pesticides act synergistically
with parasitic fungi in killing insects pests. Fungal spores, widely used
as biocontrol agents are applied in sprays and baits, and when delivered in
suspension with sub-lethal levels of pesticides are much more effective in
killing insects. Equally, Bt biopesticides enhance the killing power of parasitic
fungi synergistically. That information was transmitted through a written
question to the European Parliament .
year’s decline was serious enough and described as “beepocalypse now” by a
news report . According to the US Department of Agriculture one mouthful
in three of the foods we eat directly or indirectly depend on pollination
by honeybees . Most fruit and many vegetables would disappear from our
diet along with an immediate shortage of meat due to the loss of forage. This
winters’ bee loss was 34 percent, up from the 25 percent the previous year
The decline is attributed to
‘Colony Collapse Disorder’ (CCD), most likely to be multi-factorial. The main suspects include pesticides,
parasites, viruses, radiation from cell phone transmitters [7-9]
(Mystery of Disappearing
Honeybees, Requiem for the Honeybee,
and Vanishing Bees, SiS
34) and even brood temperature . The impact of sub-lethal levels of pesticides
on the immune system of the bee leads to synergistic infection of the bees
by fungal parasites. In addition,
the behaviour of the bees is frequently modified leading to
confusion in foraging and failure to return to the hive.
Organic farming practices that
retain more natural habitats and avoid the use of chemical pesticides should
provide environments that serve as honeybee sanctuaries from the ravages of CCD. There are scientific
studies showing that agricultural landscapes with organic crops are far superior environments for both honey-
and bumblebees [11, 12]. It would be prudent to create organic bee sanctuaries
as widely and as soon as possible.
Fungal infections more deadly with increased carbon dioxide in the atmosphere
With regard to the fungal parasites, it was recently shown that
the prominent fungal parasite Nosema ceranea has been a longstanding and widespread infection of honeybees
in the United States . Nosema ceranae was detected also in Canada . Spores of a related parasite,
Nosema apis, was found to respond
to increased carbon dioxide in the atmosphere by enhanced germination, resulting
in higher mortality of infected bees . Will global warming result in
the honeybee losing its struggle with fungal parasites?
Sub-lethal effects are the silent killers
The sub-lethal effects of insecticides
go beyond the synergistic effect of insecticides on the immune system, as
they may also affect learning and foraging competence of the honeybee, A recent
study from France showed that bees fed sub-lethal levels of Bacillus
thuingiensis Cry1Ab protein (a toxin in MON810 maize) affect food
consumption and or learning processes leading to disturbed foraging .
The neonicotinoid pesticides that also affect bees in similar ways  are
used extensively as systemic insecticides, and frequently originate from seed
treatment. One member of that group, Imidacloprid, was tested extensively,
leading to its ban in France, Another of the neonicotinoid pesticide, Acetamiprid,
was found to impair olfactory learning in the honeybee while the pesticide
Thiamethoxam did not appear to effect bee behaviour . The regulation of
insecticides should definitely be extended to include sub-lethal behavioural
impairment of the honeybees, and those insecticides having such an effect
should be banned immediately. A risk assessment to honeybees was developed
in France for non-sprayed (seed treatment)
systemic chemicals , though predictably industry
representatives argued that field test data should override trials on sub-lethal
effects . Along those lines, industry and its associated academics selected
and reviewed 25 laboratory studies showing that Bt toxins including Cry1Ab
have no adverse effects on honeybees , but the only adverse outcome considered
was mortality directly due to the pesticide, excluding learning impairments
that could also result in the bees dying. Unfortunately, regulatory agencies
appear to be similarly impaired when it comes to recognizing evidence related
to sub-lethal impairment of the bees.
Organic agriculture must be widely adopted to save the honeybee
In conclusion, sub-lethal levels of
pesticides, including the Bt biopesticides produced in genetically modified
(GM) crops covering some 30 percent of the global area, disorientate the bees,
making them behave abnormally, and compromise their immunity to infections.
Regulators have allowed the widespread deployment of systemic neonicotinoid
pesticides based on assessments of lethal dose in bees of the pesticides
alone, ignoring clear evidence that sub-lethal pesticide levels act synergistically
with fungal parasites in killing insects. The honeybees may well be succumbing
to such synergistic effects. There is every reason to eliminate the use of
all pesticides that act synergistically with parasitic fungi, and all Bt crops
should be banned for the same reason. Obviously, these problems will disappear
with the widespread adoption of organic, non-GM farming.
A., Steffan-Dewenter I. Tscharntke T. Agricultural landscapes with organic
crops support higher pollinator diversity. Oikos 2008117, 3, 354-361.
M,.Nilsson H,.Smith H. Interacting effects of farming practice and landscape
context on bumble bees Biological Conservation
2008, 141, 417-26.
Evans JD, Smith IB, Pettis JS. Nosema
ceranae is a long-present and wide-spread microsporidian infection
of the European honey bee (Apis mellifera)
in the United States. J Invertebr
Pathol. 2008 97(2), 186-8.
GR, Shafer AB, Rogers RE, Shutler D, Stewart DT. First detection of Nosema ceranae, a microsporidian parasite
of European honey bees (Apis mellifera),
in Canada and central USA. J. Invertebr
Pathol. 2008, 97(2), 189-92.
K. Influence of carbon dioxide on Nosema
apis infection of honeybees (Apis mellifera). J Invertebr Pathol. 2007, 95(2), 84-6.
R, Desneux N, Decourtye A, Chaffiol A, Pham-Delègue MH. Does Cry1Ab protein
affect learning performances of the honey bee Apis mellifera L. (Hymenoptera, Apidae)?
Ecotoxicol Environ Saf. 2008
Jan 16; [Epub ahead of print]
El Hassani AK, Dacher M, Gary V, Lambin M, Gauthier M,
Armengaud C. Effects of sublethal doses of acetamiprid and thiamethoxam
on the behavior of the honeybee (Apis
mellifera).Arch Environ Contam
Toxicol. 2008, 54(4), 653-61.
Vergnet C. Risk assessment to honey bees: a scheme developed in France for non-sprayed systemic compounds. Pest Manag Sci. 2007, 63(11), 1069-80.
HM, Maus C. The relevance of sublethal effects in honey bee testing for
pesticide risk assessment.Pest Manag Sci. 2007, 63(11):1058-61.
Marvier M, Huesing J, Dively G, Huang ZY. A meta-analysis of effects of
bt crops on honey bees (Hymenoptera:
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