Acaricidal and disinfectant compositions for treating pests on plants, animals and human beings comprise an active ingredient of general formula <FORM:0638662/VI/1> where R1 and R2 represent hydrogen or a methyl group; R3 represents hydrogen or an alkyl group, R4 represents a phenyl radical, substituted if desired, with non-salt-forming groups, alone or with other effective substances, in admixture with at least one inert solid, or semi-solid, or not easily inflammable liquid, diluent or carrier, characterized in that the said active ingredient is finely divided, the particle size being below 300 microns.  Such amides are prepared by the methods disclosed in Specification 615,137, [Group IV (b)].  For the preparation of dusts the active agent and the carrier, either separately or in admixture, may be milled to the required degree or the finely ground carrier may be impregnated with a solution of the active material in a volatile solvent which is subsequently removed.  Fine dispersions are also obtained by emulsifying the active agent or a solution thereof.  Aerosols are produced by dissolving in an inert carrier such as difluodichloro-methane which boils below room temperature at atmospheric pressures.  The inert solid carriers comprise materials of inorganic or vegetable nature, e.g., tricalcium phosphate, calcium carbonate, kaolin, bole, bentonite, talcum, calcined magnesia, kieselguhr, boric acid, powdered cork and powdered wood, which may be employed in admixture with wetting or dispersing agents.  Inert liquids comprise oils of vegetable origin, e.g., castor and solvents such as carbon tetrachloride, ethylene dichloride, tetrachlorethane, hydrogenated naphthalenes, alkylated naphthalenes, solvent naphtha and the like.  Dispersing or emulsifying agents comprise natural or synthetic soaps, turkey red oil, fatty alcohol sulphonates, sulphated fats, esters of fatty acids, high molecular quaternary ammonium compounds and condensation products of aliphatic or araliphatic compounds and ethylene anide.  The products may include additives such as casein, salts of fatty acids, glue, resins, fats, albumen degradation products, solubility promotors, dyestuffs and perfumes. Other organic synthetic acaricides, insecticides, oricides, fungicides or bactericidal substances may be added, e.g., benzyl benzoate, dimethyl thianthrene, phthalonitrile, a a -bis (p-chlorophenyl) b b b  trichlorethane, b b -dichlorethane, 4:6-dinitro-o-cresol, mixtures of nitrated naphthylamines, mercury compound, copper compounds and sulphur. For special purposes semi-solid carriers of the nature of a cream, ointment, paste or wax may be employed into which the active substance can be worked with or without the aid of solubility promotors and/or of emulsifying agents. Such carriers are typified by soft soap and petroleum jelly. Materials suitable for incorporating in veterinary preparations comprise paraffin oil, vegetable oils, e.g., olive, castor, sesame and camphor oils, glycerine, petroleum jelly, wool fat and emulsifying agents such as soaps, sulphonated fats, fatty acid esters, fatty alcohol sulphonates, alkylated aromatic and halogenated aromatic sulphonic acids, higher molecular alkoxy carboxylic acids and esters of phosphoric acid.  Emulsions of ointment-like consistency may be produced by employing stearic acid and fatty acid salts, e.g., sodium stearate.  For fat-free ointments, cellulose ethers, aluminium hydroxide gel and the like may be used.  Talcum, starch, lactose and the like may be added.  The bactericidal action may be increased by the addition of phenols, e.g., p-chlor-m-cresol, o-butyl p-chlor phenol, o-benzyl p-chlorphenol, cyclohexylphenol, dodecyl-benzyl-trimethyl-ammonium metho sulphate, oxyquinoline derivatives, colloidal silver preparations and thiocyanic acid. Specified active materials of the invention are the anilide, -N-methyl and ethyl o- and ptoluidides, N-ethyl M-toluidide, -N- methyl and ethyl anilide, -N- methyl and ethyl o-chloranilide, -N-ethyl p-bromanilide, -N- ethyl 3,4 dichloranilide, -N- ethyl 2 chlor 6 methyl anilide, o-anisidide, -N-methyl p-anisidide, -N-ethyl o-anisidide, -N- isoamyl o-toluidide -N-ethyl p-phenetidide of crotonic acid; and b ,b -dimethylacrylic acid and trimethyl acrylic acid derivatives similar to the crotonic acid derivatives above.