Cypermethrin is a synthetic pyrethroid used as an insecticide in large-scale commercial agricultural applications as well as in consumer products for domestic purposes. It behaves as a fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when applied to indoor inert surfaces. Exposure to sunlight, water and oxygen will accelerate its decomposition. Cypermethrin is highly toxic to fish, bees and aquatic insects, according to the National Pesticides Telecommunications Network (NPTN). Cypermethrin is a broad-spectrum insecticide, which means it kills beneficial insects and animals as well as the targeted insects. Fish are particularly susceptible to cypermethrin. Resistance to cypermethrin has developed quickly in insects exposed frequently and can render it ineffective.