Novel substituted N-pyridylmethyl-N'-cyanoisothioureas of formula ##STR1## wherein R is C.sub.1 -C.sub.4 alkyl, cyclopropyl or benzyl; R.sub.1 is C.sub.1 -C.sub.4 alkyl or cyclopropyl; X is halogen; and n is the integer 0, 1, 2 or 3.Processes for the preparation of these compounds, the corresponding starting materials and intermediates and the use of the novel compounds in pest control, especially for controlling insects and representatives of the order Acarina, especially insect pests in rice crops, and as starting materials for the synthesis of novel pesticidal compositions are described.