Clothianidin is a synthetic insecticide that belongs to the neonicotinoid class of chemicals, which are designed to protect crops from various insect pests. As a systemic insecticide, it is absorbed by a plant and then distributed throughout its tissues, including roots, stems, leaves, pollen, and nectar. This internal distribution allows the plant itself to become toxic to insects that feed on any part of it.
How Clothianidin Affects Insects
Clothianidin acts by disrupting the central nervous system of insects. It specifically targets nicotinic acetylcholine receptors (nAChRs), which are proteins on nerve cells responsible for transmitting signals. When clothianidin binds to these receptors, it mimics the natural neurotransmitter acetylcholine, but unlike acetylcholine, it does not release from the receptor, causing continuous overstimulation of the nerve cells.
This sustained stimulation leads to a breakdown in normal nerve signal transmission, resulting in paralysis and, ultimately, the death of the insect. This mechanism provides effective control against a wide spectrum of sucking and chewing insects.
Commercial and Residential Uses
Clothianidin is widely applied in agriculture and horticulture to manage various insect pests. A primary application method involves treating seeds, particularly for major crops such as corn, canola, and soybeans. The insecticide is absorbed by the seedling as it grows, providing protection from early-season pests.
Beyond seed treatments, clothianidin is also used as a soil drench, where it is applied to the soil around plants, allowing roots to absorb it. It can also be applied as a foliar spray directly onto plant leaves. This insecticide is found in some consumer products for managing pests in lawns and ornamental plants.
Impact on Non-Target Organisms
Despite its targeted action on insect pests, clothianidin can have unintended consequences for non-target organisms in the environment. A significant concern is its impact on pollinators, particularly honey bees and wild bees. Bees can be exposed to clothianidin through contaminated pollen and nectar from treated plants, as well as through dust generated during the planting of treated seeds.
Exposure to clothianidin can lead to sublethal effects in bees, such as impaired navigation, reduced foraging efficiency, and a weakened immune response, making them more susceptible to diseases. Chronic exposure can also affect larval development and queen bee reproduction, potentially harming colony health. In high enough concentrations, it can be directly lethal to bees.
The persistence and mobility of clothianidin in the environment mean it can leach into groundwater or run off into surface waters. This can pose a risk to aquatic invertebrates, which are a foundational part of aquatic food webs.
Additionally, small birds and mammals can be affected by ingesting treated seeds found on the soil surface. While generally considered non-toxic to birds in acute doses, chronic exposure through a diet of treated seeds may present a toxic risk to smaller bird species. This accumulation can lead to reproductive and developmental issues in exposed wildlife.
Global Regulations and Restrictions
Concerns regarding the environmental impact of clothianidin have led to various regulatory actions worldwide. In the European Union, the European Food Safety Authority (EFSA) concluded that most outdoor uses of neonicotinoid pesticides, including clothianidin, pose a risk to wild bees and honeybees. This assessment led to a ban on all outdoor uses of clothianidin across the European Union.
In the United States, the Environmental Protection Agency (EPA) oversees the registration and regulation of clothianidin. While not subject to a complete ban, the EPA has acknowledged its persistence and potential for mobility in the environment, with concerns about leaching to groundwater and runoff to surface waters. The EPA concluded that clothianidin is likely to adversely affect a significant percentage of federally listed endangered or threatened species and their critical habitats. The agency also recommends specific precautionary labeling to mitigate risks to pollinators.