Clothianidin is a synthetic insecticide, developed jointly by Takeda Chemical Industries and Bayer AG. It belongs to the neonicotinoid class of chemicals, structurally similar to nicotine. Neonicotinoids were developed as an alternative to older insecticide classes like organophosphates and carbamates, addressing issues such as rapid environmental degradation and lack of selectivity. This provided a more stable and targeted pest control option in agriculture.
Mechanism and Agricultural Application
Clothianidin functions as a neurotoxin, targeting the central nervous system of insects. It binds to nicotinic acetylcholine receptors (nAChRs), proteins that normally receive signals from the neurotransmitter acetylcholine. Clothianidin mimics acetylcholine, activating these receptors but disrupting normal nerve impulse transmission. This leads to hyperactivity, paralysis, and eventual death.
The chemical is characterized by its systemic nature, meaning it is absorbed and distributed throughout a plant’s tissues, including roots, stems, leaves, pollen, and nectar. This systemic property ensures that the entire plant becomes toxic to insects that feed on it, offering prolonged protection against various pests. Clothianidin is extensively used in agriculture, primarily as a seed treatment for major crops.
Treating seeds before planting provides early and sustained protection against a wide spectrum of sucking and chewing insects, such as aphids, whiteflies, and beetles, in crops like corn, soybeans, canola, wheat, and barley. Beyond seed treatments, clothianidin is also applied as a foliar spray or soil drench. It can also be found in certain residential and commercial products used for controlling pests like bedbugs and ants, or for protecting turf and ornamental plants.
Impact on Pollinators
The widespread application of clothianidin has generated substantial concern regarding its documented impact on pollinating insects, particularly honey bees and various species of wild bees. Pollinators encounter clothianidin through several routes of exposure. During the planting of treated seeds, fine dust abraded from the seeds can become airborne and drift significant distances, contaminating nearby flowering plants and directly exposing foraging bees. Additionally, bees can ingest the insecticide when they collect contaminated pollen and nectar from treated crops or surrounding vegetation that has absorbed the systemic chemical.
Exposure to clothianidin can lead to both acute and sublethal effects on bee populations. Acute toxicity can result in immediate bee mortality, even at low concentrations, through both contact and oral exposure. Sublethal effects, occurring at lower, non-lethal doses, are particularly detrimental to colony health. These include impaired navigation, hindering their return to the hive, and reduced foraging efficiency, reducing food gathering.
Chronic exposure to clothianidin residues in pollen and nectar can weaken bees’ immune systems, increasing vulnerability to diseases and parasitic infections. These effects can compromise the health and viability of entire bee colonies, contributing to reduced brood production and colony decline. These impacts are linked to the global decline observed in both managed and wild pollinator populations.
Effects on Other Non-Target Organisms
Beyond its documented impacts on pollinators, clothianidin poses risks to a broader array of non-target organisms. Its systemic nature and environmental persistence allow it to migrate beyond the initially treated plants, affecting numerous beneficial insects. For instance, predatory insects that consume pests containing clothianidin can experience secondary exposure through their diet, potentially disrupting natural biological pest control mechanisms.
Clothianidin also exhibits high toxicity to aquatic invertebrates, a foundational part of many freshwater food webs. Runoff from agricultural fields where clothianidin has been applied can transport the chemical into rivers and streams. This contamination can harm sensitive aquatic insect larvae, such as mayflies and caddisflies, thereby diminishing the food supply for fish, amphibians, and other aquatic wildlife. Terrestrial organisms, including birds, also face risks of exposure.
Birds, especially insectivorous species or those consuming treated seeds directly from fields, can be exposed to clothianidin. Ingesting treated seeds can lead to direct poisoning, causing disorientation, reduced feeding, and impaired reproduction. Secondary exposure can also occur when birds consume contaminated insects, illustrating its broad ecological footprint across different trophic levels.
Human Health Considerations and Regulatory Status
From a human health perspective, clothianidin is specifically engineered to target the nervous system of insects, which differs physiologically from the mammalian nervous system. As a result, it generally presents lower acute risks to mammals, including humans, when compared to older classes of pesticides like organophosphates and carbamates. Nevertheless, ongoing scientific research continues to assess potential long-term effects associated with environmental exposure and the presence of residues in food products.
The regulatory status of clothianidin varies across international jurisdictions. The European Union has adopted a restrictive stance, banning all outdoor uses since 2018. This decision was driven by scientific evidence of its detrimental effects on pollinator populations. Conversely, the U.S. Environmental Protection Agency (EPA) has maintained conditional approval for clothianidin, with an ongoing registration review process.
The EPA’s approach includes establishing guidelines and restrictions to mitigate environmental risks. While the EPA announced an interim decision allowing continued use, it has also moved to cancel the registrations for some formulations containing clothianidin or similar neonicotinoids. This divergence underscores differing interpretations and assessments of scientific findings concerning clothianidin’s environmental and public health implications.