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Insecticides and bees: your questions answered

Live online Q&A

Dr Ian Bedford, Dr James Cresswell, Professor Lin Field and Professor Dave Goulson answered your questions about the effects of neonicotinoids on bee populations on Tuesday 19th March 2013. This discussion was tweeted under #plantsci. Find out more about our panel here. We've compiled the tweets from the Q&A on Storify.

If you have a question on a plant science related issue then get in contact with our plant science panel via Twitter, @senseaboutsci using #plantsci, or email us at


15. "Farmers use large amounts of insecticides but are obliged to keep within guideline limits. Gardeners use less, but will invariably use more than is needed ("just for luck!"), and represent a much larger customer base. Whose use do you think will have the bigger overall impact on insects?" Rachel Roberts

IB: Although the range of insecticides and use rates are less for home garden / amateur use, than professional use, there is always the potential for over-use in home gardens, and little can be done to regulate this.  The most commonly available chemical insecticides for home use are either pyrethroid/pyrethrum based or neonicotinoids, both of which can have detrimental effects on a wide range of insects, including bees.  Pyrethroids are generally short persistence whilst the neonicotinoids are systemic and therefore are often very persistent.  Ironically, a lot of insecticide use at home is not necessary, particularly where small localised infestations of pests can be removed by hand or with physical contact products.


14. "What pesticides do bee keepers have available to use for active pest management in controlling Varroa mites etc. in hives?" Rob Yorke

IB: Pyrethroids have been used to try and control Varroa mites, but these are no longer deemed effective due to mites becoming resistant. Oxalic acid and Thymol are being used by bee keepers as an alternative. New products that stimulate bees to clean themselves of mites are currently being tested - John Innes Centre entomologists now have a project to investigate the effectiveness of some of these.


13. "Perhaps a neonicotinoids ban is a kneejerk reaction, but shouldn't we be more determined to find alternatives to pesticides?" Rebecca Nesbit

DG: Personally, I would not describe a ban as kneejerk – neonics have been in use for 20 years, and several hundred scientific studies of their impacts have been published over that period. EFSA spent 6 months reviewing this evidence and concluded that neonics pose an unacceptable risk when used on flowering crops or when sown at times of year when bees are active (due to dust created in sowing). A major problem is that there is almost no funding for research into biological or cultural controls (e.g. crop rotations), since these do not offer a return on investment (you cannot patent a crop rotation system). Instead industry puts huge amounts of money into developing and promoting technological solutions such as new pesticides, GM crop varieties etc. which they can then sell for decades to come.

JC: There has been a low intensity of industry-sponsored research into the impacts of pesticides to date, perhaps in part because the regulatory hurdles to get approval of pesticides have been low. The new approval guidelines may have the salutary effect of requiring industry to have a deeper fundamental understanding of its products. I hope this leads to more funding for basic science from the pesticide producers.


12. "Could these foreign bred bees carry foreign pests and diseases of bees to the UK?" Bug Mann

IB: I assume you are referring to the mass-produced bumblebees that are imported for pollination of horticultural crops. If so, there are production procedures and protocols in place to ensure that no transfer of pests and diseases occurs when they are imported to other countries.  However, I don't know how often colonies are checked or how stringently this is policed.


11. "Bees were clearly in huge decline before neonicotinoids. Are there estimates on how much is due to habitat loss vs pesticides?" Rachael Ludwick

DG: Sadly, there are no such estimates, and they would be near impossible to obtain. Bees and other beneficial wildlife have declined due to a raft of adverse changes to the environment from 1940-2000 which one could broadly call intensification: loss of hedges, drainage of marshes, conversion of haymeadows and downland to monocultures, availability of pesticides, fertilizers etc. Since all these things changed at the same time, working out which is most important is pretty much impossible.


10. "Do we have definitive evidence that neonicotinoid seed treatments lead to decreased bee numbers in a field situation?" Andrew Barr

JC: There is no definitive evidence yet of these kinds of impacts from neonicotinoids consumed by bees in nectar and pollen under field conditions. For honey bees, field trials have not detected detrimental effects from foraging in treated crops, though some of these trials may not been sensitive enough to pick up an effect. For bumblebees, decisive field trials have yet to be completed (the recently published scientific results have all involved ‘artificial’ forms of dosing). There have, however, been effects observed on honey bees from neonicotinoids that were released in dust during the seed-planting process.


9. "I have heard there is a 'foreign' bee called the tree bumblebee and it is spreading rapidly in this country. Why was this introduced from abroad? Why is it increasing and not being killed by the poisonous oilseed flowers? Is this a threat to our bumble bees and will it breed with them? Will this bee able to pollinate the same crops if other bumble bees become extinct?" Betty McLean

IB: The tree bumblebee Bombus hypnorum has indeed spread across much of southern Britain over the past decade. As its name suggests, it usually nests in holes in trees rather than in the ground like other species. The tree bumblebee poses no threat to our other native species and will not interbreed with them. The fact it is doing so well is probably an indication that the habitats it exists within are also in good health. This species also produces much larger colonies than most of our other native species.


8. "Is it possible that wildflower margins become polluted with neonicotinoid pesticides from over spray, drift or dust and the perennial plants there accumulate a higher concentration of neonicotinoids and increased toxicity?" Phill Clayton

JC: I am unaware of research into neonicotinoid accumulation in perennial plants over successive years. My guess is that neonicotinoids are unlikely to increasingly accumulate in perennial plants because the neonicotinoids will be continually lost in parts of the plant that are shed (e.g. when leaves are dropped) and diluted as tissues grow.


7. "Many reports about insect decline refer to habitat loss as an explanation, for example the recent Butterfly Conservation report on moths. Yet habitat loss in Britain has been reversed in recent years (more awareness, tree planting conservation efforts, agri-environment scheme etc.) so there has been an unequivocal improvement in the physical habitats for insect over the last decade. But insect populations have continued to decline. Neonicotinoid use is the new factor in this time period. Why do so many reports focus on habitat rather than insecticides?" Biff Vernon

IB: It is very true that habit loss is being addressed by the creation of new ones. However, for the complex ecosystems to recover it can take many, many years. This is especially so if the new habitats don't connect to existing ones. We need to ensure that 'green-bridges' are in place to allow species to disperse throughout, and to the new locations. Our home gardens are a ideal starting point!

DG: I agree entirely. It is hard to explain continuing declines in farmland moths, butterflies, birds, bees and beetles (every group for which we have long-term data), despite an annual spend of ~£500 million of tax-payers money on agri-environment schemes. Overuse of persistent pesticides would seem to me to be a plausible candidate for the explanation (or at least part of it).


6. "Given that the French government banned the use of neonicotinoids for use as seed treatments on maize, oilseed rape and sunflowers for at least a year (indeed it may still be ongoing), did that have any effect on the health of commercial honey bees or even wild bumble bees that the ban was imposed to help?" Alan Dewar

JC: I am not aware that follow-up studies have been either conducted or published.


5. "Are the alternatives to neonicotinoids better for bees?" Andrea Quigley ‏

DG: The disadvantage of neonics (compared to the alternatives) is that they are highly persistent in the environment (lasting for years in soil), and being systemic they get into pollen and nectar of crops such as oilseed rape. When used as a seed treatment they have to be applied prophylactically, since the farmer cannot know in advance what pest problems he may have. This is very like taking antibiotics as a precaution against disease – it means that they are overused, and that resistance is likely to develop. In fact there is little or no convincing published evidence that neonicotinoids are the most cost-effective means of pest control for UK agriculture, and much of their current usage may prove to be entirely unnecessary. Hence I would question the premise that an alternative is needed at all.

LF: Alternative ‘conventional’ insecticides will potentially pose the same risk. But non-conventional control strategies could be developed. These might include the use of trap crops, companion planting, pheromones or manipulation of crops to deter pests either by conventional breeding or genetic modification. These are all approaches being studied at Rothamsted Research.


4. "Would you be able to provide me with the key publications from which this debate (on both sides) is happening? How solid on both sides is the science behind these studies?" Alistair Griffiths

LF: Providing key publications requires an exhaustive trawl of the literature which I cannot claim to have done so I can’t do this. I would direct you to the DEFRA review of last autumn (see link) which reviewed what they considered to be the key publications and concluded that:

• "Some of the new studies provide evidence of sub-lethal effects of neonicotinoids in the conditions applied in the research."

• "However, none of the studies gives unequivocal evidence that sub-lethal effects with serious implications for colonies are likely to arise from current uses of neonicotinoids."

• "Existing studies submitted to support current regulatory approvals fully meet current standards. They do not explicitly address all the sub-lethal effects suggested by the academic research. However, they do cover a wide range of important endpoints and, in these studies, hives exposed to treated crops did not show any gross effects when compared to control hives exposed to untreated crops."


3. "While it may be that neonicitinoid pesticides are all or part of the reason for colony collapse disorder, isn’t it the case that the cause of the slow diagnosis and slow reaction to the problem is due to underinvestment in agricultural research in the UK and across Europe? (I think there are statistics on declining spending on public sector agricultural research – but I don’t have them to hand)." Rob Moss

IB: The short answer is 'Yes'.  The quantity of research undertaken is always limited by the funds that are available and this applies across many disciplines. We certainly have the resources and the expertise to undertake much more research within the UK and across Europe as and when the funding becomes available. Unfortunately, the current economic climate has a significant effect on what can be achieved at the moment.

DG: As a scientist, I’m prone to agree that we need more funding for research generally! It has become extremely hard to obtain funds, and I spend about 50% of my time writing grant applications, the large majority of which I can expect to be rejected. Science funding is an easy thing to reduce when times are hard, but the long-term repercussions of underinvestment in science are likely to hamper our economic recovery and leave us behind other rapidly developing nations.

JC: The slow recognition of the potential impacts of neonicotinoids on bee health originates in part from the previously blunt regulatory testing, which focussed only on honey bees.  Improved procedures for pesticide approval are now being drawn up in the new EU guidelines by EFSA (European Food Safety Authority).  Most of the drive to study pollinator declines and the new scientific insights into potential causes have come from ecologists and ecotoxicologists in universities.  As ever, more research needs more funding in these directions.


2. "In view of the immense threats that these pesticides pose to human health and the environment, is it not about time to tell prevaricating scientists that they should get lost?" Dr. H. A. (Henk) Tennekes

LF: Neonicotinoids do not pose an ‘immense threat to human health’. They have been developed precisely because they control pest insects but have low toxicity to mammals. This is because they act by binding to a particular protein in insects but bind much less effectively to the equivalent protein in mammals. Such selective insecticides are much better than the older, more generally toxic compounds. In addition, if they are used within controlled areas and under the manufacturers' guidelines, there should be no significant effects on the environment.

JC: Scepticism is integral to science and should not be mistaken for prevarication. The eminent physicist Richard Feynman reportedly said, "Science is a way to teach how something gets to be known, what is not known, to what extent things are known (for nothing is known absolutely), what the rules of evidence are, how to think about things so that judgements can be made ..." I think Feynman means that doubt is essential to the scientific process. If you lose the sceptics, you lose the science. Scientists would change their view if evidence to the contrary was found. Like the great 20th Century evolutionist J.B.S. Haldane, I’d give up on evolution tomorrow if somebody finds a fossil rabbit in the Cambrian (i.e. in very ancient geological rocks).


1. "Neonicotinoids are shown to cause paralysis and death in insects (including bees) at low levels. Isn't that enough evidence [to ban their use]?" Kirsty Jean Jackson

LF: If the question is 'CAN neonicotioids cause paralysis and death in bees?' then the answer is yes. But if the question is 'DO they do this when used according to the recommendations of the manufacturers?' then the answer is 'no'. The guidelines have been drawn up to prevent effects on non-target organisms. So ‘potential toxicity’ alone is not enough to warrant a ban. A ‘precautionary’ ban may sound reasonable but must be weighed against the need to control insect pests that damage crops.

DG: All insecticides kill bees, but we cannot ban them all. What we must consider is whether typical doses encountered by bees in the field are sufficient to kill them or cause them significant harm (through sublethal impacts on egg-laying, navigation, learning etc..). However, in my view, the balance of evidence suggests that neonicotinoids are likely to be impacting significantly on wild bees such as bumblebees, and I fully support the partial ban proposed by the EU. 

JC: The current uncertainty about the impact of neonicotinoids on bees centres on the environmentally realistic dosage, which is certainly ‘low’, but may be lower than the ‘low’ dosage used in most experiments. The actual residues of pesticides that bees consume in nectar are very poorly known – for example we only have fragmentary data for the UK.  Additionally, biology and natural history may still hold surprises - for example, bees may have the capacity to detoxify neonicotinoids or to recuperate after a treated crop has flowered.  Or, as found in a recent field trial, bees may not collect their forage from exactly where we expect. These gaps in our knowledge mean that there’s not yet a clear evidence-based assessment of the level of harm that the neonicotinoids can cause.

IB: Neonicotinoids are toxic to a wide range of invertebrates but unfortunately can't discriminate between those that are pests and those that are not. Other regularly used pesticides are also toxic to bees. The problem facing growers is that they needto have effective ways of preventing plant pests from decimating their crops in order to sustain their livelihood and our food security. Whilst safer, or more specific alternatives are being sought, we need to ensure that the products that adversely affectbeneficial insects are applied so as to minimise their adverse effects.