Abstract: A device destined for the emission of vapors of an active substance, in particular an insecticidal substance, is described which comprises, in a rigid assembly,A. a reservoir containing the active substance and having an evaporation surface for the emission of the active vapors, said reservoir comprisingI. a system of two plates of a porous or fibrous material, one of the large faces of one of the plates facing one of the large faces of the other, and a frame for the plates which separates the space between the two plates from the exterior while leaving entirely or partially free at least one of the two large external faces of the two plates, which can thus serve as an evaporation surface, andIi. an insecticidal organo-phosphorus substance having a vapor pressure, at 25.degree. C, of between 5 .times. 10.sup.-.sup.5 and 5 .times. 10.sup.-.sup.3 mbar, with or without addition of a pyrethrinoid insecticidal compound having a vapor pressure, at 25.degree. C, of between 1 .times. 10.sup.-.sup.6 and 2 .times. 10.