Neonicotinoids: Chemistry, Agricultural Use, and Environmental Impact
Neonicotinoids, often referred to as "neonics," are a prominent class of neuro-active insecticides. Developed by scientists at Shell and Bayer during the 1980s, these chemicals are structurally similar to nicotine. While nicotine was used as an insecticide for centuries, it was eventually banned in the early 21st century, paving the way for the widespread adoption of neonicotinoids in modern agriculture and veterinary medicine.
Because they target the central nervous system of insects, neonicotinoids are highly effective at controlling a wide variety of pests. They are used extensively in crop protection and are also employed in veterinary applications for controlling ticks and fleas.
Key Facts
- Chemical Basis: Neonicotinoids are neuro-active compounds chemically similar to nicotine.
- Primary Use: Widely used in crop protection and veterinary flea/tick control.
- Mechanism: They act on the central nervous system of insects.
- Systemic Nature: They are water-soluble and can be absorbed throughout a plant's tissues.
- Leading Product: Imidacloprid was the most widely used insecticide globally from 1999 through at least 2018.
Chemical Generations and Market Presence
The neonicotinoid market is divided into different generations of chemical compounds. The first generation established the foundation for widespread use, while more recent generations have been introduced to the market.
First-Generation Neonicotinoids
The initial wave of these insecticides includes several well-known compounds:
- Acetamiprid
- Clothianidin
- Dinotefuran
- Imidacloprid
- Nitenpyram
- Nithiazine
- Thiacloprid
- Thiamethoxam
Second-Generation Neonicotinoids
More recently marketed compounds include:
- Cycloxaprid
- Imidaclothiz
- Paichongding
- Sulfoxaflor
- Guadipyr
- Flupyradifurone
The following table provides a breakdown of major neonicotinoid products and their market turnover as of 2009:
| Name | Company | Products | Turnover (Million US$) |
|---|---|---|---|
| Imidacloprid | Bayer CropScience | Confidor, Admire, Gaucho, Advocate | 1,091 |
| Thiamethoxam | Syngenta | Actara, Platinum, Cruiser | 627 |
| Clothianidin | Sumitomo Chemical / Bayer CropScience | Poncho, Dantosu, Dantop, Belay | 439 |
| Acetamiprid | Nippon Soda | Mospilan, Assail, ChipcoTristar | 276 |
| Thiacloprid | Bayer CropScience | Calypso | 112 |
| Dinotefuran | Mitsui Chemicals | Starkle, Safari, Venom | 79 |
| Nitenpyram | Sumitomo Chemical | Capstar, Guardian | 8 |
Agricultural Application and Systemic Properties
One of the defining characteristics of neonicotinoids is their systemic nature. This means the chemical can move through the entire plant. They are frequently applied to seeds as a prophylactic (preventative) treatment before planting to protect against herbivorous insects.
Because neonicotinoids are water-soluble, they are absorbed by the plant as it takes in water during growth. Once absorbed, the pesticide becomes present in all parts of the plant, including the leaves, flowers, nectar, and pollen. They can also be applied directly to the soil.
Environmental and Wildlife Impact
While effective against target pests, neonicotinoids can also affect non-target insects due to their impact on the central nervous system. This has led to significant scientific and regulatory scrutiny regarding their effect on various ecosystems.
Impact on Bees and Pollinators
There is substantial evidence regarding the risks neonicotinoids pose to pollinators. Studies have indicated that these chemicals can impair honeybee flight ability and negatively affect bumblebee colony growth and queen production. Furthermore, neonicotinoids have been detected in the nectar of treated crops and in significant portions of the world's honey supply.
Broader Wildlife Concerns
Beyond bees, the environmental footprint of these chemicals extends to other wildlife:
- Birds: Research has explored links between insecticide use and declines in bird populations.
- Other Wildlife: There are concerns regarding the impact on invertebrate die-offs and potential negative effects on monarch butterfly populations in the USA.
- Mammalian Systems: Scientific studies have investigated the potential harms to mammalian nervous systems.
Frequently Asked Questions
How do neonicotinoids work in plants?
Neonicotinoids are water-soluble. When applied to seeds or soil, the developing plant absorbs the chemical through its roots as it takes in water, distributing the pesticide throughout its tissues, including leaves and flowers.
What is the difference between first and second-generation neonicotinoids?
First-generation neonicotinoids include established compounds like imidacloprid and clothianidin. Second-generation compounds, such as sulfoxaflor and flupyradifurone, are more recently marketed versions of these neuro-active insecticides.
Why are neonicotinoids considered systemic?
They are considered systemic because, once absorbed by the plant, the chemical is present in all parts of the organism, including the nectar and pollen, rather than just staying on the surface of the leaves.
What are the primary uses for these chemicals?
They are primarily used for crop protection in agriculture to prevent damage from herbivorous insects, and in veterinary medicine for the control of fleas and ticks.
How do they affect insects?
Neonicotinoids act on the central nervous system of insects, which can lead to death or other deleterious (harmful) effects in both target pests and non-target species.