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Pests > Pest Management > Chemical control > Synthetic pesticides > Insecticides > Imidacloprid > Neonicotinoids, are there substitutes? India
May 2013. A question was asked by a member from India about the availability of substitutes for imidacloprid (neonicotinoids insecticides)?
A member gave a very detailed answer to this question, which provided information on the unique characteristics of the neonicotinoids as a group of insecticides. This is what was said, with only slight editing:
Finding an alternative to neonicotinoids is not as simple as saying “ho hum” and looking at the APVMA website. They have unique characteristics that have stabilized specific areas of crop production and I know of no single active ingredient that will substitute. Neonicotinoids have characteristics that are akin to those of the ideal pesticide. When applied sensibly as recommended they are toxic to a limited range of organisms that includes insects and excludes mammals, earthworms, fish, in fact most others (and, sadly, Lepidoptera in the case of imidacloprid). They are both contact and systemic via the roots and foliage and have about a 40 day half life in the ‘field’. I know of experiments that have induced neonicotinoid resistance in insect populations, but I cannot remember reports of any field cases. In my professional life in India we found they can be applied as a dust to peanut seeds and they protected the young roots and pods from soil insect pests (white grubs and termites) that decimate crops – at the same time checking aphid, jassid and thrip activity in the foliage. They broke down well before the crop was harvested. Similarly, a small amount applied to cotton seed protected the young crop from aphids but did not hurt the natural enemies of the boll worms that came later. There are similar stories from other climes and crops. In this role, they replaced the ops, carbamates, pyrethroids and worse that had induced so many chronic pest problems. I encountered imidacloprid in the late 80s early 90s which probably means it has been around for 25-30 years. If it has such a dire effect on bees it would have eliminated them by now – well before the colonies started to die in recent epidemic proportions. I share the view of the UK scientists that there is much more to this issue than we currently understand. The original story was that a student had discovered that bees exposed to nectar with levels of neonicotinoid that were at the lower detectable level – about 10 parts per billion – lost the ability to pass on direction finding information to other colony members. Good work – but I believe follow up research was not conclusive.
A useful article on the effect of neonicotinopids on bumblebees can be found in a New Scientist article, see below.
Bees need Europe’s pesticide ban, whatever the UK says
A European Union ban on the neonicotinoid pesticides thought to harm bees is good news, despite British reluctance, says biologist Dave Goulson
Yesterday the European Commission decided to impose a ban on the use of neonicotinoid pesticides in the European Union. These chemicals will now be banned for two years for crops that attract bees. All EU nations, even the UK and the others that voted against this move this week, must impose the ban by December this year.
I was very sceptical when I was first asked to support such a ban. The idea is that neonicotinoids – a family of pesticides designed to kill crop pests such as aphids – are responsible for the worrying decline in bee numbers over the last decade or so.
Having previously been asked to sign up for campaigns claiming that the bee problem was due to mobile phones, genetically modified crops, overhead power lines, and various other eccentric or implausible notions, I suspected that the neonicotinoid hypothesis was just the latest on the list. However, a review of the science suggested that there was something worth investigating.
The issue has focused largely on harm the neonicotinoid chemicals clothianidin, imidacloprid and thiamethoxam might be doing to bees, both domestic honeybees and wild pollinators such as bumblebees.
Neonicotinoids are widely applied as a seed dressing to crops such as oilseed rape, and being systemic they spread through the plant into the nectar and pollen. They are highly toxic to insects: for example the “LD50” – the dose that kills half of test subjects – in honeybees is about 4 billionths of a gram.
To put that in context, 1 gram – little more than the weight of a sachet of salt – would provide an LD50 to 250 million honeybees, or roughly 25 metric tonnes of bee. They are neurotoxins, binding to neural receptors in the brain and causing swift paralysis and death.
Until recently, there had been few studies of the effects of neonicotinoidson my own specialism, bumblebees. All were small scale and nearly all performed in cages or glasshouses. Taken together, they seemed to suggest that exposure to very low levels, such as might occur when a bee fed on a treated oilseed rape crop, was not sufficient to kill many bees, but it seemed to affect their behaviour, particularly their ability to learn, gather food and navigate.
None of the safety tests on which pesticides are judged fit for use assess these abilities. What is more, they are likely to be much more important in the field than in small-scale test environments: in the open, bees perform astonishing feats of navigation and learning when gathering food from flowers. It seemed to me, and to other researchers around the world, that there was a need to study what these sublethal effects might be doing to bee colonies in natural situations.
We carried out our investigations in 2011 and published them last year(Science, DOI: 10.1126/science.1215025). We exposed bumblebee nests to the concentrations of neonicotinoids found in the pollen and nectar of oilseed rape for two weeks, and then placed the nests out in the field to see how they fared compared with control nests. Over the next six weeks the treated nests grew more slowly, and ultimately produced 15 per cent as many new queens.
Since our study, work from other labs has confirmed that field-realistic doses greatly reduce pollen collection in bumblebee workers, potentially explaining why our treated nests performed poorly. It has also been found that concentrations of neonicotinoids as low as 1 part per billion in their food cause a drop in egg-laying in bumblebees of 30 per cent. Considerably higher concentrations than this have been found in the pollen of treated crops.
For bumblebees, the evidence so far is convincing and coherent: exposure to levels of neonicotinoids commonly found in crops profoundly damages colony success. The only study that appears to contradict this was recently placed online by the British government’s Department for Environment, Food and Rural Affairs. It describes a study the department conducted last year In which it attempted to repeat our work but with the pesticide exposure phase of the experiment occurring in the field.
The researchers placed bumblebee nests next to the only untreated field of oilseed rape they could find, and next to two other fields treated with two different neonicotinoid pesticides, and followed the colonies over time.
However, the experiment had shortcomings that make the conclusions unreliable. There was only one example of each condition – the untreated field and the two treated fields – and, disastrously but interestingly, the control nests all became contaminated with the pesticides. The summary of this report claims the study shows no clear effect of neonicotinoids on bumblebee colonies: that is hardly surprising, given the absence of any controls, and it is hardly the sort of evidence one would wish a government to base its policies upon.
Perhaps the most valuable lesson to be learned from this work is that bumblebee nests placed in the landscape become contaminated with multiple types of these chemicals, even on farms where none is used. Many of the nests had concentrations of neonicotinoids higher than 1 part per billion, and most had detectable levels of at least two different types.
While the debate so far has focused on bees, there are broader issues to consider. These chemicals last in soils for a long time, and evidence has recently emerged that they accumulate over time (PLoS One, 10.1371/journal.pone.0029268). This is likely to be enough to affect soil life profoundly.
A common argument in favour of neonicotinoids is that they provide economic benefits, and that alternative pest-control methods are worse. But studies from US, for example, show that yields of soya bean do not benefit at all from dressing seed with neonicotinoids, despite this being standard practice (Journal of Economic Entomology, DOI: 10.1603/ec11429). Sadly, similar experiments in the UK have not been conducted. Given that farmers get most of their technical advice from pesticide companies, it is reasonable to suppose that a good proportion of UK pesticide use may be unnecessary.
The European Food Safety Agency spent six months evaluating the evidence and concluded that current use of neonicotinoids poses unacceptable risks. The British parliament’s Environmental Audit Committee agreed. Numerous non-governmental organisations, including the Royal Society for the Protection of Birds, which is normally very cautious, followed suit. What was once a radical stance is now where the vast majority of informed opinion lies; but the British government stands apart.
However, after yesterday’s European Commission decision the British government will have to implement the moratorium nevertheless. Perhaps this imposed mass field trial will finally provide the evidence to convince it and other doubters to accept the growing signs that neonicotinoids are at least partly to blame for the decline of our most vital pollinators.
Correction:When this article was first published, a different study concerning neonicotinoid persistence in soils was mentioned.
Dave Goulsonis a biologist at the University of Sussex in Brighton, UK. His new book on bumblebees, A Sting in the Tale, has just been published