Tag Archives: thiamethoxam

Bees and neonicotinoids – another twist in the tale.

To the agrochemical companies and to many farmers they are essential tools ensuring efficient crop production. To environmentalists and to many bee scientists they are dangerous chemicals contributing to declining bee populations. I am talking, of course, about the neonicotinoid insecticides widely used in this country to control insect pests.

Last week two papers were published on-line in the journal Nature emphasising the dangers posed by these chemicals.

One paper, from a team at Newcastle University, investigated whether honeybees and bumblebees showed any preference (positive or negative) for food containing neonicotinoids; there had been suggestions that bees might avoid neonicotinoid-treated crops in the field. The new lab-based work showed that, when offered a choice, bees preferred to eat sucrose solution (nectar) containing neonicotinoids (imidacloprid or thiamethoxam) rather than control sucrose solution. If this occurs in the field then bees may forage preferentially on crops containing chemicals toxic to their health and inadvertently bring back these toxins to their nests.

The second paper, from scientists at Lund University in Sweden, showed that the neonicotinoid clothianidin, when used in the field, damaged wild bee (bumblebee and solitary bee) populations but was without effect on honeybees. I want to focus on this paper as it is the first controlled study of the effects of a neonicotinoid on honeybees, bumblebees and solitary bees under field conditions. Let’s start by looking at the background.

Three years is a long time in science

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Back in 2012, two studies were published showing that neonicotinoids, even when they didn’t kill bees, could affect bee behaviour in a way that impaired survival of honeybee and bumblebee colonies. The findings showed that these chemicals could contribute to a decline in the numbers of bees and other pollinators. These observations had a big effect on policy and indirectly contributed to the current partial ban on the use of three neonicotinoids in Europe.

One of the papers was from Dave Goulson’s lab, then at Stirling, and found that even at the low doses typically encountered on treated crops in the field, neonicotinoids substantially reduced the number of queens produced by bumblebee colonies, so impairing survival. In Goulson’s study, bumblebees were treated with neonicotinoids in the lab before being allowed to fly freely. This is called a semi-field design and some have suggested that the findings cannot be extrapolated to the real world. The levels of neonicotinoids have also been criticised although these were very carefully thought through.

There was considerable media interest in this work, nicely described in Goulson’s latest book (A Buzz in the Meadow) and the UK Food and Environment Agency (FERA) labs in York hastily set up a preliminary field trial to examine the problem. During the spring and summer of 2012 they studied three fields of oil seed rape, one treated with the neonicotinoid, imidacloprid, another treated with the neonicotinoid, clothianidin and a third untreated field to act as a control. Bumblebee (Bombus terrestris) nests were placed by each field and the occupants were left to fly freely and build their colonies. Extensive analyses were performed including colony growth, the pollen collected by the bees and pesticide residues detected in pollen and nectar.

Superficially this sounds like a rigorous study (free flying bees, compare neonicotinoid-treated with control, plenty of analyses and so on) and it should have given an indication of the effect of neonicotinoids under real-world field conditions. The success of the trial depended on the bees foraging on the crop near their nests so there should have been clothianidin-exposed colonies, imidacloprid-exposed colonies and neonicotinoid-free controls. Unfortunately the bees had other ideas; they largely ignored the flowering oil seed rape by their nests, foraging further away and returning with pollen from crops treated with another neonicotinoid, thiamethoxam. This completely negated the original design so that, in my view, no valid conclusions can be drawn from the study, despite official pronouncements.

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The new Swedish study

The FERA work was a valiant but flawed attempt to study the effects of neonicotinoids on bumblebees under field conditions and it was clear that a properly conceived field trial was required. The ambitious new study from Lund University mostly fills that void.

The Lund team selected 16 landscapes surrounding spring-sown oil seed rape fields in different parts of southern Sweden in 2013. The landscapes were divided in to 8 pairs on the basis of the nature of the surrounding countryside and for each pair one was sown with seed treated with the neonicotinoid, clothianidin and the other was sown without neonicotinoid, to act as a control. All seed also contained a fungicide. The neonicotinoid-treated seed also contained a pyrethroid to protect plant roots but there was no evidence that the bees came in to contact with this chemical.

Honeybee hives, bumblebee (Bombus terrestris) colonies and solitary bee (Osmia bicornis) cocoons were placed by each field during the flowering season and their progress was followed. Additionally, the numbers of free flying wild bees (bumblebee and solitary bee) were assessed at each field during the flowering season. Pollen brought back by bees was analysed for flower type and for pesticide residues. The study was large enough to allow statistical analyses to be performed so that valid conclusions could be drawn although the design was unable to detect effects smaller than 20%.

Unlike the FERA study, bees did forage on the oil seed rape adjacent to their colony based on pollen analysis, although this was not an exclusive choice. Bees near treated fields brought back pollen and nectar containing clothianidin whereas those near untreated fields did not. The study design seemed to have been successful and the results were clear:

1. Honeybee hives behaved similarly by treated and untreated fields; there was no effect of the pesticide on colony strength. This is good news for honeybees and for beekeepers and agrees with a 2014 field study from Canada also using clothianidin.

2. Bumblebee colony growth and reproduction were reduced near treated fields. This agrees with earlier semi-field studies so that it is now difficult to avoid the conclusion that agricultural use of neonicotinoids has damaging effects on bumblebees.

3. Whereas solitary bees placed by untreated fields emerged from cocoons and built new nests, this did not occur for cocoons situated near treated fields, possibly because of navigational problems caused by insecticide exposure.

4. The number of free-flying wild bees was reduced by about 50% at the treated fields.

The implications of the new Swedish study

Honeybees were not affected by foraging from a neonicotinoid-treated crop whereas wild bees (bumblebees and solitary bees) suffered reductions in numbers and reproductive ability. Wild bees are, therefore, more sensitive to neonicotinoids than honeybees. This may be because, as James Cresswell at Exeter has shown, honeybees break down neonicotinoids more quickly than bumblebees so that honeybees experience lower doses.

The effect of the neonicotinoid on wild bees is an important result for several reasons. Wild bees are important pollinators, contributing more than half of the “pollination service” required for crops. Crop yield and quality will suffer if these insects are lost so we need to look after them and that may need to include rethinking use of pesticides.

The differential sensitivity of bee types to neonicotinoids shows that environmental risk assessment of new and existing insecticides, typically performed in short term lethal studies on honeybees, is inadequate to determine long term effects on different bee types in the field.

These new data will add to the pressure to extend the European moratorium on the use of three neonicotinoids as seed dressings after the initial two year period ends in December. There is, however, concern that if neonicotinoids are not available then farmers will use older insecticides that may be more dangerous for bees. Perhaps farmers should rethink their use of pesticides and return to a “treat when required” policy rather than using neonicotinoids prophylactically.

When the three neonicotinoids were temporarily banned in 2013, farmers claimed that the yields of crops would be drastically reduced. It is interesting that in the first season when crops were grown from untreated seed in the EU, the yields actually increased. Perhaps we should rethink the use of chemicals more generally in modern farming.

500 dead bumblebees – the chemical blitz of modern farming

In September I wrote about the mysterious death of 500 bumblebees. New information has emerged about this incident so I have rewritten the post:

Earlier this year, Sheila Horne was walking at Hacton Parkway, a public park and conservation area in Havering, East London. April is normally a good time to see insects in their prime so she was very surprised to find many dead and dying bees near the path. She alerted local naturalist, Tony Gunton who identified the insects as bumblebee queens from three species, red-tailed, buff-tailed and common carder. This was not a minor incident, there were as many as 500 bees affected.

Chemical analysis of the dead bees

Natural England was appointed to investigate the insect deaths and samples of dead bees were sent to FERA in York for analysis. The results were released in August and showed that the bees were contaminated with the neonicotinoid insecticide imidacloprid and two fungicides, flusilazole and epoxiconazole. Imidacloprid can be very poisonous to bees and bumblebees are more susceptible to this chemical than honeybees. Imidacloprid is currently subject to a two year partial ban for some agricultural uses in the EU. Neither fungicide on its own is especially toxic to bees although flusilazole was phased out this October because of its high toxicity to fish and because of other potential toxic effects.

A nearby field of oil seed rape as the source of the chemicals?

The chemical analysis raises two questions. Where did the bumblebees pick up these chemicals? Were these chemicals responsible for the bee deaths?

Neither question can be answered definitively but as so many dying bees were found together in one place, it seems likely that the source of the poisoning was close by. Hacton Parkway lies alongside arable farmland and at the time of the poisoning some of the land was planted with flowering oil seed rape, so it is a reasonable conclusion that the bees had been feeding there. Because of the chemical analysis, it was initially assumed that the crop had been planted using seed treated with imidacloprid ahead of the ban and that the imidacloprid had killed the bees. Natural England have recently concluded their investigation and found that in fact the seed used to plant the crop had been treated with another neonicotinoid, thiamethoxam. Neither imidacloprid nor epoxiconazole had been used on the crop and the last spraying with flusilazole was in November 2013. Analysis of the dead bees for thiamethoxam failed to detect any of the chemical but this could have been due to losses before the analysis.

What killed the bees?

So, why did these bees die? Because there are so many unanswered questions we cannot be sure. The dead bees were contaminated with imidacloprid but the oil seed rape crop was not the source. We can only assume that the bees fed elsewhere on imidacloprid-treated crops and were flying with this chemical in their systems. It is known that at typical field concentrations, imidacloprid does not kill bumblebees.

There is also the question of how the bees were exposed to the two fungicides if the oil seed rape had not been sprayed with these chemicals during the flowering season. As with the imidacloprid, we have to assume that the bees were exposed elsewhere. It is possible that the fungicides weakened the bees or made them more susceptible to the neonicotinoids. There is some evidence for such interactions for other insecticide/fungicide pairings.

Because the bees died close to the treated crop, the focus of lethality has to be on the thiamethoxam, now known to have been used on the oil seed rape. Although thiamethoxam is indeed an insecticide, there is evidence from one lab-based study and another field study (albeit lacking controls) that, at field-realistic concentrations, thiamethoxam is not lethal to bumblebees. I find it unlikely, therefore, that thiamethoxam alone killed the bees, providing the farmer followed safety guidelines.

We shall never know what actually happened at Hacton Parkway but my best guess is that these bees were flying with the three chemicals in their system and encountered the thiamethoxam-treated oil seed rape. When they fed from it, they picked up the additional neonicotinoid. Two neonicotinoids, with perhaps synergistic effects of the fungicides, were too much and they died.

The investigation is now closed!

The investigation is now closed and it will be impossible to resolve the many questions raised by this incident, which is a pity. Despite this uncertainty, the results of the chemical analysis stand. These bees died with three chemicals in their bodies: one neonicotinoid and two fungicides. They were also exposed to a second neonicotinoid. This was no laboratory experiment; this reflects what is happening around us when these chemicals are used. Have a look at this report to see more evidence of the widespread use of chemicals in UK farming. Our agricultural practices have led to this chemical blitz and the result is the deaths of important pollinators. How often is this occurring on a lower level but not being noticed or reported?

I should like to thank Tony Gunton (local naturalist) and Helen Duggan (Press Officer, Health and Safety Executive) for sharing information about this incident.

Fields of Gold or Killing Fields?

Rapeseed is a major cash crop in the UK and elsewhere in Europe, so when you see those familiar strips of yellow in the late spring – think profits for farmers.  Rapeseed is heavily treated with insecticides and fungicides – so also think profits for agrochemical companies.  One of these insecticides, the improbably named Cruiser OSR, is a big earner for the agrochemical company Syngenta.  In a surprise move last week, the French Minister of Agriculture has issued a warning that he intends to revoke the licence for Cruiser OSR.   This story has hardly featured in the UK press but it has considerable significance. 

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One of the active ingredients in Cruiser OSR is thiamethoxam, a member of the class of neonicotinoid insecticides that act by poisoning the nervous system of insect pests.   These insecticides are used either as seed dressing or as systemic treatments.  Either way the compound is present throughout the plant and available to kill insect pests.

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Not all insects are pests, however.  Bees perform a crucial role in pollinating crops and without bees food would be much more expensive and the countryside would look very different.   Evidence has been accumulating that, as well as killing insect pests, the neonicotinoid insecticides can have harmful effects on bees.   In crops treated with these insecticides the harmful chemical is present throughout the plant and may be picked up by bees when they forage for pollen or nectar.  Rapeseed, for example, provides an important source of food for bees when they emerge after winter.  If the crop has been treated with Cruiser OSR then it is likely that bees will feed on contaminated pollen and nectar and may pick up the thiamethoxam.

In Italy it was found that when maize seed coated with the insecticide imidacloprid  (another neonicotinoid)  began to be used there were bee deaths coincident with sowing.  Most likely, dust from the treated seeds was contaminating land used by bees.  When the use of neonicotinoid-coated maize seed was banned in Italy these bee deaths did not occur.    France and Germany have joined Italy in banning the use of some neonicotinoids  as seed dressing also because of effects on bees.     

The agrochemical companies claim that these insecticides are safe for bees if used properly but new research published earlier this year showed that under field conditions and at sub-lethal doses, the neonicotinoids can have serious effects on the ability of bees to navigate and may affect the survival of bee colonies.  The response of DEFRA in this country was as follows: “We have considered all recently published studies and have concluded that they do not present any new evidence”.

In France, the response has been different.  The National Agency for Safety of Food and the Environment (ANSES) was asked to report on the significance of the new work.  ANSES concluded that the new studies did provide evidence of a threat and the Minister acted accordingly.

Syngenta has responded to the proposed ban on Cruiser OSR:  “This is a dark day for French and European agriculture – 30% of rapeseed will be lost”

Bees are under pressure from many influences including loss of habitat, climate change, hive pathogens and insecticides.  If France considers these insecticides to pose a threat to bees, I do hope DEFRA will now reconsider the effects of these compounds on bees in the UK.