At least six species of insects have developed significant levels of pyrethroid resistance in the field in the U.S., including: a cockroach, Blatella germanica; a leafmining fly, Liriomyza trifolii; the Colorado potato beetle: Leptinotarsa decemlineata; the horn fly, Haematobia irritans; the pink bollworm, Pectinophora gossypiella; and the house fly, Musca domestics. For each of these species, laboratory tests have confirmed resistances first detected as control failures in the field. Both metabolic and target site mechanisms have been found in these species. Resistance generally appeared within about 20-30 generations of intense field exposure to pyrethrins, permethrin or fenvalerate.