PROBLEM TO BE SOLVED: To provide a pest control method of arthropods by gene silencing; to provide a protection method of arthropods to parasites and predators; and to provide transgenic predators expressing polyribonucleotide structure (dsRNA) molecule formed by single self-complementary RNA chain or at least two complementary RNA chains. SOLUTION: To deliver dsRNA to arthropod tissues, an arthropod is contacted with dsRNA to the arthropod and/or the dsRNA is directly fed to the arthropod. The method is useful for determining biological functions of the gene of the arthropod. COPYRIGHT: (C)2009,JPO&INPIT