Neonicotinoid pesticides kill bees

SOURCE: Ken Taylor (
SUBHEAD: Fresh evidence links neonicotinoid pesticides to death of the honeybee spurs calls for banning the pesticides.

 Dr. Mae-Wan Ho on 24 January 2011 for ISIS - 

Image above: Bayer's miracle - "A simple method of insect control consists of drenching the soil around a tree with a product containing Imidacloprid." From (  

Increase vulnerability to infection at minute doses
The honeybee’s vulnerability to infection is increased by the presence of imidacloprid, even at the most microscopic doses. This new research result by Dr Jeffrey Pettis and his team at the US Department of Agriculture’s Bee Research Laboratory has remained unpublished for nearly two years, according to an ‘exclusive’ report in UK’s newspaper, The Independent [1].

Increased disease infection happened even when the levels of the insecticide were so tiny that they could not be detected in the bees that the researchers had dosed. The neonicotinoid insecticides, introduced since the early 1990s, are increasingly used on crops in the US, Britain and around the world. Bayer, the German chemicals giant that developed the insecticides insists that they are safe for bees if used properly, but they have already been widely linked to bee losses. Imidacloprid was Bayer's top-selling insecticide in 2009, earning the company £510 m.  

Link to colony collapse of the honeybee
 Neonicotinoids have attracted growing controversy since their introduction by Bayer in the 1990s, and have been blamed by some beekeepers and environmental campaigners as a potential cause of Colony Collapse Disorder (CCD), first observed in the US in 2006, in which bees disappear from hives en mass (see [2] Mystery of Disappearing Honeybees, SiS 34). Prof. Joe Cummins at ISIS was among the first to link neonicotinoid insecticides to CCD ([3]

Requiem for the Honeybee , SiS 34); which had led to swift action on the part of the German Government in banning the pesticides ([4] Emergency Pesticide Ban for Saving the Honeybee, SiS 39). Between 20 and 40 per cent of American hives have been affected, and CCD has since been observed in several other countries from France to Taiwan, though it has not yet been detected in Britain [1], where the area of cropland treated with neonicotinoids has gone from 0 in 1993 to more than 2.5 m acres in 2008.

 Neonicotinoids bans
The chemicals have been banned already in France, Germany and Italy. In Britain, the Co-op has banned their use in farms from which it sources fruit and vegetables, but the British Government has refused to ban or suspend them. Buglife director, Matt Shardlow, commented on the Pettis study: “This new research from America confirms that at very, very low concentrations neonicotinoid chemicals can make a honeybee vulnerable to fatal disease. If these pesticides are causing large numbers of honeybees, bumblebees, solitary bees, hoverflies and moths to get sick and die from diseases they would otherwise have survived, then neonicotinoid chemicals could be the main cause of both colony collapse disorder and the loss of wild pollinator populations.
"The weight of evidence against neonicotinoids is becoming irresistible – Government should act now to ban the risky uses of these toxins."
The UK Government is to debate the impact on bees and other insects of the new generation of pesticides linked to bee mortality [5]. The Government will be called on to suspend all neonicotinoid pesticides approved in British, pending more exhaustive tests of their long-term effects on bees and other invertebrates. The subject will be raised in an adjournment debate in the House of Commons Tuesday 25 January 2011 on a motion tabled by Martin Caton, the Labour MP.

Caton, a former agricultural scientist said the evidence is growing that neonicotinoids were a problem, but the testing regime for the compounds in Britain and Europe was not rigorous enough. “I think they should be suspended on the precautionary principle while we improve it.” He added: “We’re talking about a threat to our whole ecosystem, when invertebrates are being lost at the sort of rate that has happened in recent years.” There is already a call for banning neonicotinoid pesticides in the US and European Union that has attracted 1 069 781 signatures so far [6]  

Unpublished research repeated and published in France
 Dr Pettis told The Independent his research was completed almost two years ago [1], “but it has been too long in getting out.” He has now been submitted his manuscript to a new journal for publication. However, in a comment to the news article, Pettis made clear that he is not alleging that his research is being suppressed, but that “the review process on the paper has simply been lengthy.” Pettis and a member of his team, Dennis van Engelsdorp, of Penn State University, both leaders in research on CCD, and have spoken about it at some length in a film about bee deaths that has been shown widely in Europe, but not yet in Britain or the US.

 In "The Strange Disappearance of The Bees", made by the American film-maker Mark Daniels, Pettis and van Engelsdorp reveal that they exposed two groups of bees to the well-known bee disease agent Nosema. One of the groups was also fed tiny doses of imidacloprid. There was a higher uptake of infection in the bees fed the insecticide, even though it could not subsequently be detected, which raises the possibility that such a phenomenon occurring in the wild might be simply undetectable. Although the US study remains unpublished, French researchers at the National Institute for Agricultural Research in Avignon have independently carried out similar research and published their study in the journal Environmental Microbiology. They stated [7]: “We demonstrated that the interaction between nosema and a neonicotinoid (imidacloprid) significantly weakened honeybees.”  

Synergistic effects between pathogen and pesticide confirmed
The results of the French group confirmed that synergistic effects between Nosema and neonicotinoid pesticide weakened the honeybee, causing increased mortality [7]. The activity of glucose oxidase, which enables the bees to sterilize colony and brood food, was significantly decreased only by the combination of both compared with controls, not with the two groups treated singly by either Nosema or neonicotinoid pesticide.

This synergistic effect was first suggested by Prof. Joe Cummins writing for ISIS ([8] Parasitic Fungi and Pesticides Act Synergistically to Kill Honeybees? SiS 35). Such an effect is well-known and already exploited in controlling pests. To reduce harm caused by chemical pesticides, more ‘eco-friendly’ biological controls have been developed using microbial pathogens including viruses, bacteria and fungi, especially fungi.

When fungal pathogens are administered with sub-lethal doses of pesticides, they interact synergistically and result in much more effective killing of insect pests such as termites, thrips, and leaf-cutter ants. Imidacloprid, a systemic neonicotinoid pesticide is widely used around the world on food crops, and has been implicated in the loss of honeybee in France, where one hive in two contain residues of imidacloprid, 30 percent of honey and 26 percent of bees, albeit at sub-lethal levels of about 5 mg/kg. Simultaneously, a parasitic microsporidia fungus, Nosema ceranae, has been associated with bee losses in the USA, and Spain.

This prompted the researchers in Avignon to carry out their investigations. The study was designed to look at possible effects on 1) individual mortality and energetic demands; 2) individual immunity; and 3) social immunity. Energetic demands were assessed by sucrose consumption as Nosema alters host nutrient store and feeding behaviour. Individual immunity was assessed by total haemocyte (blood cell) count (THC) and phenoloxidase (PO) enzyme activity. PO plays a central role in invertebrates’ immune reaction, being involved in the encapsulation of foreign object through melanisation. THC gives an indirect measure of basal cell immune activity as the blood cells are involved in phagocytosis and the encapsulation of a parasite.

Glucose oxidase (GOX) enzyme activity is measured as an indicator of social immunity, as it is involved in sterilizing the colony, and its antiseptic product, hydrogen peroxide is secreted into larval food and honey to inhibit pathogen development. The results showed that imidacloprid significantly increased mortality over controls even at the lowest concentration used (0.7 mg/kg), but mortality was always highest when the bees were simultaneously exposed to Nosema. At the lower concentrations previously designated sub-lethal (0.7 and 7 mg/kg), the synergistic effects of the pesticide with Nosema were additive; but at the highest concentration of imidacloprid (70 mg/kg), the effects were closer to multiplicative.

Sucrose consumption showed a similar pattern. THC and PO, as indicators of individual immunity were not significantly affected by the treatments, though the possibility remains that they may not be adequate indicators of individual immunity. However, glucose oxidase, as indicator of social immunity, was significantly decreased only when imidacloprid and Nosema were present together. This decrease in social immunity could explain the higher mortalities in bees simultaneously exposed to the two agents.  

 1. “Exclusive: Bees facing a poisoned spring”, Michael McCarthy, The Independent, 20 January 2011,

2. Ho MW and Cummins J. Mystery of disappearing honeybees. Science in Society 34, 35-36, 2007.

3. Cummins J. Requiem for the honeybee. Science in Society 34, 36-37, 2007.

4. Ho MW. Emergency pesticide ban for saving the honeybee. Science in Society 39, 40-41, 2008.

5. “Call to ban pesticides linked to bee deaths”, Michael McCarthy, The Independent, 21 January 2011,

6. American bee emergency – act now., accessed 21 January 2011,

7. Alaux C, Brunet J-L, Dussaubat C, mondet F, Tchamitchan S, Cousin M, Brillard J, Baldy A, Belzunces LP and Le Conte Y. Interactions between Nosema microspores and a neonicotinoid weaken honeybees (Apis millifera). Environmental Microbiology 2010, 12, 774-82.

 8. Cummins J. Parasitic fungi and pesticides act synergistically to kill honeybees? Science in Society 35, 38, 2007.


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