The present invention relates to a method for combating insects or arachnids which comprises contacting the insects or the arachnids, their habitat, breeding ground, food supply, plant, seed, soil, area, material or environment in which the insects or the arachnids are growing or may grow, or the materials, plants, seeds, soils, surfaces or spaces to be protected from insect or arachnid attack or infestation with a pesticidally effective amount of a compound of the general formula (I) or a salt thereof wherein: Ar is a cyclic radical, n is 0 or 1, X is CO or SO.sub.2 and R.sup.1 to R.sup.4 are as defined in claim 1.