Neonicotinoid Insecticides
Introduction
Neonicotinoid insecticides, often referred to as "neonics," are a class of neuro-active insecticides chemically similar to nicotine. They were developed in the 1980s and 1990s by Shell and Bayer, respectively. The use of neonicotinoids has been associated with beneficial effects, such as improved crop yield and quality, but their impact on non-target organisms and ecosystems has raised significant environmental and ecological concerns.
Chemistry
Neonicotinoids are synthetic compounds that share a common mode of action that affects the central nervous system of insects, leading to paralysis and death. They are much less toxic to mammals and birds than they are to insects because of differences in the nervous systems. The chemical structure of neonicotinoids is similar to that of nicotine, hence the name. There are several types of neonicotinoids, including imidacloprid, clothianidin, and thiamethoxam, each with different properties and uses.
Mode of Action
Neonicotinoids act on the nicotinic acetylcholine receptors (nAChRs) in the insect's central nervous system. They are agonists, meaning they increase the action of these receptors, leading to an overstimulation of the nervous system. This overstimulation causes paralysis and eventual death in insects. Unlike other insecticides, neonicotinoids are systemic, meaning they are absorbed by the plant and distributed throughout its tissues, including the pollen and nectar. This makes them highly effective at controlling sucking and chewing insects, but it also means they can affect non-target insects that feed on the plant's nectar or pollen.
Use and Application
Neonicotinoids are used in a variety of agricultural and non-agricultural settings. They can be applied as a seed treatment, soil drench, or foliar spray, and they are used to control a wide range of pests, including aphids, whiteflies, thrips, and beetles. Because of their systemic nature, they provide long-lasting protection against pests. However, their widespread use has led to concerns about their impact on non-target organisms and the environment.
Environmental Impact
The environmental impact of neonicotinoids is a subject of ongoing research and debate. Their systemic nature means they can be present in all parts of the plant, including the pollen and nectar, which can be consumed by non-target insects such as bees. There is evidence to suggest that exposure to neonicotinoids can have sub-lethal effects on bees, affecting their foraging behavior, reproduction, and survival. There are also concerns about the impact of neonicotinoids on aquatic ecosystems, as they are highly water-soluble and can leach into water bodies.
Regulatory Status
The regulatory status of neonicotinoids varies by country. In the European Union, the use of three neonicotinoids (imidacloprid, clothianidin, and thiamethoxam) was restricted in 2013 due to concerns about their impact on bee health. In 2018, these restrictions were extended to include all outdoor uses. In the United States, the Environmental Protection Agency (EPA) is currently reviewing the registration of several neonicotinoids.