The invention relates to compounds of the general formula ##STR00001## in which R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, W, X, A.sub.1, A.sub.2, a, b and c are as defined in the specification, and to any enantiomers thereof. The active ingredients have advantageous pesticidal properties. They are particularly suitable for controlling parasites in warm-blooded animals.