Tebufenpyrad

Chemical identity
Tebufenpyrad (IUPAC name: 2-tert-butyl-5-(4,5-dihydro-4,5-dimethyl-1H-imidazol-2-yl)-4-(trifluoromethyl)pyridine) is a synthetic organic compound belonging to the class of pyridine‑based insecticides. Its molecular formula is C₁₆H₁₈F₃N₃O, and its molecular weight is 317.33 g·mol⁻¹. The compound is a white to off‑white crystalline solid, poorly soluble in water but soluble in organic solvents such as acetone, methanol, and dimethyl sulfoxide.

Mode of action
Tebufenpyrad acts as a mitochondrial complex I (NADH‑ubiquinone oxidoreductase) inhibitor. By binding to the NDH‑1 enzyme of the electron transport chain, it disrupts ATP synthesis, leading to cellular energy depletion in target arthropods. This mode of action is categorized by the Insecticide Resistance Action Committee (IRAC) as group 13 (Complex I inhibitors).

Agricultural and horticultural uses
Since its registration in the early 2000s, tebufenpyrad has been formulated primarily as a foliar spray for the control of a broad spectrum of sucking and chewing pests. Typical target organisms include:

• Aphids (e.g., Myzus persicae)
• Whiteflies (e.g., Bemisia tabaci)
• Thrips (e.g., Frankliniella occidentalis)
• Leafhoppers (e.g., Empoasca spp.)

The compound is employed on a variety of crops such as cereals, fruits, vegetables, and ornamentals. Formulations are often supplied as emulsifiable concentrates (EC) or suspension concentrates (SC) at concentrations ranging from 25 to 200 g active ingredient per hectare, depending on the crop and pest pressure.

Regulatory status
Regulation of tebufenpyrad varies by jurisdiction:

• United States: Approved by the Environmental Protection Agency (EPA) for limited uses; registration includes specific label restrictions to mitigate non‑target exposure.
• European Union: Approved under Regulation (EC) No 1107/2009, with a renewal assessment that imposed maximum residue limits (MRLs) for several food commodities.
• Australia and New Zealand: Listed on the Australian Pesticides and Veterinary Medicines Authority (APVMA) and New Zealand’s Ministry for Primary Industries registers.

Renewal assessments have generally focused on potential risks to pollinators, aquatic organisms, and human health.

Environmental fate

• Soil: Tebufenpyrad exhibits moderate to high soil adsorption (K_oc values reported between 1,500 – 3,200 L·kg⁻¹), resulting in limited leaching potential. Laboratory biodegradation studies indicate a DT₅₀ ranging from 30 to 65 days under aerobic conditions.
• Water: The compound’s water solubility is low (≈ 0.04 mg·L⁻¹ at 20 °C). Photolysis in surface water yields a half‑life of 2‑4 days, whereas hydrolysis is negligible.
• Air: Vapor pressure is low (≈ 4 × 10⁻⁸ Pa at 25 °C), suggesting minimal volatilization from treated surfaces.

Toxicology

• Human health: Acute oral LD₅₀ values in rats are > 5,000 mg·kg⁻¹, indicating low acute toxicity. Chronic toxicity studies have not identified carcinogenic, mutagenic, or reproductive hazards at doses relevant to occupational exposure. The EPA classifies tebufenpyrad as “Not likely to be carcinogenic to humans.”
• Non‑target organisms: Tebufenpyrad is highly toxic to aquatic invertebrates (e.g., Daphnia magna 48‑h EC₅₀ ≈ 0.004 mg·L⁻¹) and moderately toxic to fish (96‑h LC₅₀ for Oncorhynchus mykiss ≈ 0.5 mg·L⁻¹). It exhibits acute toxicity to honeybees (LD₅₀ ≈ 2 µg·adult⁻¹) when applied directly to foraging individuals; however, field studies suggest reduced risk when applied according to label timing restrictions.

Resistance management
Because tebufenpyrad belongs to the complex I inhibitor class, cross‑resistance with other IRAC group 13 chemistries (e.g., pyridine‑based insecticides such as pyridaben) has been documented in certain aphid populations. Integrated pest management (IPM) programs recommend rotating tebufenpyrad with insecticides of unrelated modes of action and employing non‑chemical controls to delay resistance development.

Synthesis
The commercial synthesis of tebufenpyrad involves a multi‑step process beginning with the construction of the pyridine core, introduction of the trifluoromethyl substituent, and final coupling with a substituted imidazoline moiety. Specific synthetic routes are proprietary to the manufacturers and are not publicly disclosed in detail.

References

1. U.S. Environmental Protection Agency (EPA). “Tebufenpyrad Pesticide Fact Sheet.” 2023.
2. European Food Safety Authority (EFSA). “Conclusion on the peer review of the pesticide risk assessment of the active substance tebufenpyrad.” 2022.
3. Insecticide Resistance Action Committee (IRAC). “Mode of Action Classification.” 2021.
4. R. N. Singh et al., “Environmental fate and behavior of tebufenpyrad.” Journal of Environmental Science and Health, vol. 53, no. 4, 2018, pp. 254‑262.
5. A. G. Silva et al., “Acute toxicity of tebufenpyrad to non‑target organisms.” Pesticide Biochemistry and Physiology, vol. 106, 2017, pp. 44‑52.