##STR1## in which each of R
1 and R
3 , independently of the other, is hydrogen or C
1 -C
4 alkyl; R
2 is hydrogen, C
1 -C
4 alkyl, benzyl or picolyl; or R
2 and R
3 are together a -(CH
2 )
4 - or -(CH
2 )
5 - radical; X is halogen; and n is an integer 0, 1, 2 or 3; and the salts of compounds of formula I; with the execption of N-picolyl-N'-cyanoguanidine and N-picolyl-N'-methyl-N"-cyanoguanidine. Also described are processes fot 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, particularly insect pests in rice crops.