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The first phenylpyrazole (IRAC subgroup 2B) insecticide, fipronil ( 1 ), was introduced in 1993 and still commands 85% of the fiprole market, with many crop, urban pest management, turf and ornamental, and animal health uses. The second major fiprole, ethiprole ( 2 ), was launched in 2005, with an improved environmental safety profile and a broader crop pest spectrum, but with much less activity against Lepidoptera and noncrop pests. Fiproles are versatile products, with potential for application as foliar sprays, seed treatments, baits, or directly to the soil. Fiproles are proinsecticides, containing a sulfur atom that is readily oxidized in plants, soil, and insects to the sulfone, which has been shown to increase biological activity and target site selectivity. Fiproles and their sulfone metabolites act as noncompetitive antagonists of GABA receptors, with potential for effects at other ligand-gated chloride channels. Resistance is often associated with a fitness cost, making rotation with insecticides from different IRAC groups effective in delaying or reversing resistance in populations. Discovery and development of new fiproles is continuing.