Science in Society Archive

Saving the Honeybee Through Organic Farming

Professor Joe Cummins

Synergistic effects of pesticides and parasitic fungi and worsening decline of honeybees

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 [3].

Last year’s decline was serious enough and described as “beepocalypse now” by a news report [4]. According to the US Department of Agriculture one mouthful in three of the foods we eat directly or indirectly depend on pollination by honeybees [5]. 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 [6].   

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, Mobile Phones and Vanishing Bees, SiS 34) and even brood temperature [10].  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 [13].  Nosema ceranae was detected also in Canada [14]. 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 [15].  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 [16].  The neonicotinoid pesticides that also affect bees in similar ways [2] 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 [17]. 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 [18], though predictably industry representatives argued that field test data should override trials on sub-lethal effects [19]. 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 [20], 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.

Presented at launch conference for Food Futures Now *Organic *Sustainable *Fossil Fuel Free , 22 April 2007, UK Parliament, Westminster, London

Article first published 25/04/08


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  2. Cummins J. Parasitic fungi and pesticides act synergistically to kill honeybees?  Science in Society 35, 38 2007.
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  14. Williams 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.
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  17. 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.
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  20. Duan JJ, Marvier M, Huesing J, Dively G, Huang ZY. A meta-analysis of effects of bt crops on honey bees (Hymenoptera: apidae). PLoS ONE. 2008, 3(1):e1415-

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