Fenthion (trade names include Baytex™, Baycid™, and Tiguvon™, used on livestock) was first registered domestically in 1965 by the Mobay Corp., a U.S. subsidiary of Bayer AG of West Germany. Fenthion is a contact and stomach insecticide used against many sucking, biting pests, especially fruit flies, stem borers, mosquitoes, and Eurygaster cereal bugs. In mosquitoes, it is toxic to both the adult and immature forms (larvae). Once used extensively in the U.S. for controlling intestinal worms, fenthion no longer has FDA approval due to an excess number of poisoning deaths. Like most other organophosphates, its mode of action is via cholinesterase inhibition. It was used mostly for the control of grubs and lice in beef and nonlactating cattle.