The pyrazolinone derivatives represented by the formula [I]: [wherein R1, R2, R3, R4 and R5 may be identical or different and represent independently a hydrogen atom, a halogen atom, an alkyl group, a haloalkyl group, an alkoxyl group, etc.; R6 represents an optionally substituted alkyl group, etc.; X represents an optionally substituted alkyl group, etc,; and Y represents an oxygen atom or a sulfur atom] are provided.