Abstract: The invention relates to new 1,3,4-substituted .DELTA..sup.2 -pyrazolines having an insecticidal activity. The compounds are active in particular against larvae of insects such as larvae of colorado beetle, cabbage butterfly and yellow-fever mosquito. On the basis of their activity the compounds, after having been processed to the usual compositions, may be used in controlling insects, in particular in the field of agriculture and horticulture. The dosage is 0.05-1 kg of the active substance per hectare. A most active compound is the substance 1-(4-chlorophenylcarbamoyl)-3-(4-chlorophenyl)-4-phenyl.DELTA..sup.2 -pyrazoline.