Novel 2,2-dimethyl-cyclopropane carboxylic acid derivatives of the formula ##STR1## wherein X.sub.1 and X.sub.2 are individually halogen, R.sub.1 is selected from the group consisting of halogen, alkyl of 1 to 8 carbon atoms, optionally substituted aryl of 6 to 14 carbon atoms, perfluoroalkyl of 1 to 8 carbon atoms, --CN and ##STR2## R' is alkyl of 1 to 8 carbon atoms, Y is selected from the group consisting of --SO.sub.2 Alk.sub.1, --SO.sub.2 Ar, ##STR3## Alk.sub.1 is optionally unsaturated alkyl of 1 to 8 carbon atoms optionally substituted with at least one halogen, Ar is aryl of 6 to 14 carbon atoms optionally substituted with at least one halogen Alk.sub.2 and Alk.sub.3 and Alk.sub.2 ' and Alk.sub.3 ' are optionally unsaturated alkyl of up to 8 carbon atoms optionally substituted with at least one halogen or together with ##STR4## form the rings ##STR5## wherein A is optionally unsaturated alkyl of up to 6 carbon atoms optionally substituted with at least one halogen, R" is alkyl of 1 to 6 carbon atoms no substituted or substituted with at least one functional group or aryl of 6 to 14 carbon atoms no substituted or substituted with at least one functional group and R is selected from the group consisting of hydrogen, alkyl of 1 to 8 carbon atoms and residue of an alcohol used in pyrethrinoid esters having pestioidal activity.