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Living in Cambridge, it’s very difficult to miss the current debate regarding the EU decision to ban neonicotinoid-based insecticides. The East of England is the ‘Bread basket of England’ with the majority of the UK’s cereal crops being grown in the region.

The three main neonicotinoids had already been restricted back in 2013. The EU had voted to prevent their use on flowering crops such as corn and oil seed rape. However, the decision in April of this year will ban the use of neonics in all outdoor crop applications. As you can imagine, opinions are very split on this matter. Environmentalists and organic farmers are celebrating the decision, while industrial farmers, farmers unions and the pesticide manufacturers are complaining that the decision was not based on sound science and is likely to lead to economic disaster for European agriculture. In the East of England, the sugar beet producers are feeling particularly hard done by with confusion about how using neonics on a non-flowering plant could possibly cause harm to bees.

I'd agree, insecticides are there to kill insects – so surely all insecticides kill bees? Why are neonics any worse than the others?

It's all about timing

Well, neonicotinoids work in a different way to other insecticides. Traditional bug killers are contact insecticides. You spray them on a plant and when a bug lands on it the chemical does its job and kills the bug. The insect either eats the poison or, in many cases, the poison is absorbed through the insect’s skin and kills it that way. So, when you use traditional insecticides, any bee that lands on a sprayed plant is killed there and then.

Neonicotinoids, on the other hand, are systemic insecticides. They are absorbed into the plant itself and kill the bugs when they try to take a bite out of the plant. As the name suggests, they are related to nicotine, and like the addictive poison in cigarettes, they operate on the nervous system. They bind onto receptors in the insects’ central nervous system, blocking them and causing paralysis and ultimately death. The advantage of neonics is that they can only cross the blood-brain barrier in insects, making them selective. They are significantly less toxic to birds and mammals.

So surely these are better for bees? Bees don’t munch on crops so neonics only kill the nasty bugs that try to eat the plants right?

Unfortunately, the neonicotinoids are also absorbed into the pollen and nectar that the bees forage on. And therein lies the problem…

When a bee lands on a plant that’s been sprayed with a contact insecticide it’s killed there and then. Not great, but it means that contact insecticides only kill worker bees. The drones, nurse bees and queen are safe from them. When worker bees take nectar and pollen from plants treated with neonics, they take the poison back to the hive and can kill the other bees that don’t normally come into contact with insecticides.

OK, so that’s really nasty and a good reason to stop using neonics. Besides, we can just go back to using the traditional insecticides right? Well, not quite that simple…

Evolution fights back

For one thing, organophosphate and carbamate insecticides are not so selective. They’re pretty much just as poisonous to birds and mammals. In fact, probably more so these days! You see, insects evolve pretty quickly and bug society has developed quite an impressive immunity to contact insecticides. Some bugs have grown thicker cuticles to prevent absorption. Others have learned to express more of the proteins that break down the poisons before they do their job. Bed bugs have just mutated to be genetically more resistant to the way that common pesticides work. So we can’t just go back to spraying the old pesticides because lots of them are much less effective than they used to be. (This isn’t just a problem for farmers. Pesticides like deltamethrin were a key method of controlling malaria vectors like mosquitos – which are now showing an alarming resistance too).

Environmental and organic farming supporters are also proposing a whole raft of other alternatives to neonics – crop rotation, more effective soil tilling, nematode worms… But all of these have their difficulties. Nematode worms require plentiful watering after introduction – not really in keeping with water usage controls. Crop rotation isn’t always an option – especially if all you’re geared up to grow is one crop.

So, what of the argument that neonics don’t pose a problem when they’re used on non-flowering plants?

Being precise

Well, I’ve done quite a lot of work on crop spraying technology and know that drift is a big issue. When you spray pesticides onto a crop on a windy day you can inadvertently also spray your neighbours’ crops. There’s lots of work focusing on making the droplets from crops sprayers nice and big so that the wind can’t blow them long distances.

But it turns out that neonics aren’t sprayed that often. In fact, most of the time they’re applied to the seeds before planting or applied to the soil as granules.

There have been a few well noted accidents where bee populations have been wiped out. In one case in Germany, the seed dressing didn’t have a sticky enough binder, so when the seeds were sown using a compressed air blower that sprays them onto the soil, the abrasion created a dust cloud of neonics which was blown onto a neighbouring crop of flowering canola. Kind of a perfect storm of unfortunate conditions all coming together. In response, heavier binders are now used to prevent this kind of problem from happening.

Another issue is that neonics are water soluble and get into the water system. Runoff from one field to another can transfer the problem. Contamination of aquifers is also suspected and several reports have found neonics in rivers and drinking water supplies. This obviously has the ability to spread the toxins to areas where they are absorbed by flowering plants.

There are no clear answers to the problem yet but it will definitely be important to properly monitor the effect of the ban to see if bee numbers increase as a result. This also highlights just how important the developing field of precision agriculture is going to be. We’re always going to be in a situation where we don’t learn about the dangers of common chemicals until it’s too late. So developing systems that allow us to use the absolute minimum amount of any pesticide or herbicide has got to be an important way forward for agriculture in general.

Apart from the bees, after looking into this, I’m a bit worried about neonics in general. They’re approved to be used in a mode where the plants absorb them because they are less toxic to mammals than they are to insects. But I’m still slightly concerned to find out that I’ve been eating neonics in my vegetable oil, my flour, vegetables and even honey. As a scientist I know that quantifying things is important – but I’m still a little worried by phrases like ‘less toxic’. I don’t know if banning neonics is the answer to bee colony collapse disorder – but I’m going to be more comfortable when they stop using pesticides that I can’t wash off my veg.

Author
Steve Thomas
Senior Consultant

Steve is a senior consultant in the Applied Science Group and works on integrating chemistry and materials science into product development and systems engineering.