All are true regarding DDT, Except

DDT (Dichloro diphenyl trichloroethane)It was first synthesized by a German chemist, Ziedler.Its insecticidal action was described by Paul Muller.It is primarily a contact poison.It acts on the nervous system of insects.It takes several hours to kill the insect.The residual action of DDT may last as long as 18 months.It has no repellent action on insects.As a residual spray, DDT is applied at a dosage of 100-200 mg/ sq. foot area.The formulation of choice is a 5 % suspension, 5-10 % strength for the control of lice, fleas, ticks, and bugs.