Compound of the formula (I) are disclosedArQQ.sup.1 C(.dbd.X)NHR.sup.1 (I)or a salt thereof, wherein Ar is an optionally substituted polycyclic ring system containing n rings, where n is the integer 2 or 3, at least n-1 rings being aromatic and containing one to three ring nitrogen atoms and optionally containing one or more additional heteroatoms; Q is an alkyl chain containing 1 to 12 carbon atoms and optionally containing a sulphur or one or two oxygen atoms; Q.sup.1 is a group (C(R.sup.2).dbd.C(R.sup.3)).sub.a --(C(R.sup.4).dbd.C(R.sup.5)) wherein a is 0 or 1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are the same or different, at least two being hydrogen and the other two being independently selected from hydrogen, halo, C.sub.1-4 haloalkyl; X is oxygen or sulphur; and R.sup.1 is selected from hydrogen and C.sub.1-8 hydrocarbyl optionally substituted by dioxalanyl, halo, cyano, trifluoromethyl, trifluoromethylthio or C.sub.1-6 alkoxy are described which have activity particularly against arthropod pests. Pesticidal formulations containing the compounds of the formula (1), their use in the control of pests and method for their preparation are also disclosed.