Fipronil is a broad-spectrum phenylpyrazole insecticide that is toxic to insects by contact or ingestion. Fipronil disrupts the central nervous system in insects by blocking the passage of chloride ions through the GABA receptor and glutamate-gated chloride (GluCl) channels. This causes hyperexcitation of contaminated insects' nerves and muscles. Specificity of fipronil effect on insects may come from a better efficacy on GABA receptor, but also because GluCl channels do not exist in mammals. Fipronil exhibits differential binding affinity for GABAA receptor subunits, with a higher binding affinity for insect receptor complexes compared to mammalian complexes. The lower binding affinity for mammalian receptors enhances selectivity for insects and increases the margin of safety for people and animals.
Due to this insecticidal activity, Fipronil uses vary widely, and include granular turf products, seed treatments, topical pet care products, gel baits, and liquid termiticides. Target insects include ants, beetles, cockroaches, fleas, ticks, termites, mole crickets, thrips, rootworms, weevils, locusts and other insects. Fipronil is a slow acting poison. When mixed with a bait, it allows the poisoned insect time to return to the colony or harborage. In cockroaches, the feces and carcass can contain sufficient residual pesticide to kill others in the same nesting site. In ants, the sharing of the bait among colony members assists in the spreading of the poison throughout the colony. With the cascading effect, the projected kill rate is about 95% in three days for ants and cockroaches. Toxic baiting with fipronil has also been shown to be extremely effective in locally eliminating wasps. All colonies within foraging range are completely eliminated within one week.
Wildlife impacts include the following:
- Fipronil is highly toxic to fish and aquatic invertebrates. Its tendency to bind to sediments and its low water solubility may reduce the potential hazard to aquatic wildlife.
- Fipronil is toxic to bees and should not be applied to vegetation when bees are foraging.
- Fipronil has been found to be highly toxic to upland game birds, but is practically nontoxic to waterfowl and other bird species. One of the metabolites of fipronil has a higher toxicity to birds than the parent compound itself.
- Fipronil is not toxic to earthworms
Always read and follow the label when applying fipronil, and refer to the Safety Data Sheet for more information.