What are Neonicotinoids?
Neonicotinoids (neonics) are a relatively new type of insecticide, used in the last 20 years to control a variety of pests, especially sap-feeding insects, such as aphids on cereals, and root-feeding grubs.
Neonics are systemic pesticides. Unlike contact pesticides, which remain on the surface of the treated foliage, systemics are taken up by the plant and transported to all the tissues (leaves, flowers, roots and stems, as well as pollen and nectar). Products containing neonics can be applied at the root (as seed coating or soil drench) or sprayed onto crop foliage. The insecticide toxin remains active in the plant for many weeks, protecting the crop season-long.
In the UK, five neonicotinoid insecticides are authorised for use in agriculture: acetamiprid; clothianidin; imidacloprid; thiacloprid; and thiamethoxam. They are used as:
- seed treatments for cereals and sugar beet (the widest use)
- soil treatment for pot plants in the ornamental sector
- treatment for turf in the amenity sector
- foliar sprays on apples, pears and a range of glasshouse crops
Neonicotinoids, especially seed treatments of imidacloprid, clothianidin and thiamethoxam on arable crops, have become of increasing concern to beekeepers and bee researchers in recent years with many of them suspecting that they may be connected to current bee declines.
In 2013, the European Union’s pesticide risk assessors revised their conclusions to recognise that use of these three neonics on flowering crops can pose a high risk to bees. Since then, EU countries have implemented a partial ban on imidacloprid, clothianidin and thiamethoxam use, prohibiting most uses on crops attractive to bees. These include oilseed rape, maize, sunflowers, and products sold to the public. Uses in greenhouses, winter sown cereals and as foliar sprays on crops after flowering are still permitted, while there are no restrictions on another two neonics, acetamiprid and thiacloprid.
How do Neonics Work?
Neonics affect the central nervous system of insects. They bind to receptors of the enzyme nicotinic acetylcholine, causing excitation of the nerves, leading to eventual paralysis and death. This specific neural pathway is more abundant in insects than warm-blooded animals, so these insecticides are selectively more toxic to insects than mammals.
Bees have a particular genetic vulnerability to neonics because they have more of these receptors than other insects, as well as more learning and memory genes for their highly evolved system of social communication and organisation, Unlike many insect pest species which are able to detoxify harmful chemicals, bees possess fewer genes for detoxification.
While the older organophosphate and carbamate insecticides tend to degrade quite rapidly in the environment, neonics are more persistent. Imidacloprid can last for months or years in soil and may leach into groundwater under some conditions.
Because they are biologically active at very low concentrations, neonics can be applied at much lower volumes in the field than the older groups of insecticides – in doses of a few grams, rather than kilos, per hectare of the active ingredient.
Neonics were originally welcomed as much safer for humans, livestock and birds than other insecticides. Seed treatments were seen as a more effective method of targeting pests than spraying crop foliage, and more environmentally-friendly because they can reduce the number of spray applications needed in-field. However, over time, it has become clear that they pose different and poorly understood risks to bees and other non-target invertebrates precisely because of the properties that have made them so useful to farmers: their systemic action; their persistence in crops and soil; and their potency at low concentrations. Added to this, their widespread use in many cropping systems and their unplanned presence in pollen and nectar builds up a worrying picture of low level but continued exposure for pollinators, which our regulatory risk assessment schemes are only starting to address.
Why are Neonics so Bad for Bees?
Boom in Neonics
Neonicotinoids are a rapidly growing sector of the pesticide market globally, used on more than 140 crop varieties. They are applied in a wide variety of settings against pests in soil, seed, turf, timber as well as foliar treatments for cereals, cotton, legumes, potatoes, orchard fruits, rice, turf and vegetables. They are also common in veterinary applications such as tick control and flea collars for pets.
The first compound, imidacloprid, was launched by Bayer Cropscience in 1991. Since then a further six compounds have been put on the global market. By 2008 neonicotinoids had taken a 24% share of the total insecticide market of €6.330 billion.
In the UK, the area of land treated with neonics has more than doubled between 2003 and 2013.