Trichogrammaspp． ( Hymenoptera:Trichogrammatidae) are the most-widely used egg parasitoids in China andthe world．T． ostriniae Pang et Chen is an important biocontrol agent in corn crops in our country，but differentT． ostriniaepopulations display different biocontrol efficacy． In order to make full use of the most beneficial populations，it isessential to be able to precisely discriminate between populations． However，it can be extremely difficult to distinguish different populations of the same Trichogrammaspecies by using morphological methods． In this study，random amplified polymorphic DNA markers were used to analyze genetic variations betweenT． ostriniae populations collected from Beijing， Shandong and Shanxi， and population-specific loci were thenlocated． From sequencing of population-specific loci， population-specific markers were successfully developed which were subsequently employed to determine the most effective biocontrol populations in mixed populationtesting． This method is helpful in screening for the most beneficial Trichogramma populations，and therefore plays a significant role in the application of Trichogrammaspp．to biocontrol． Key words Trichogramma ostriniae，random amplified polymorphic DNA，RAPD，sequence characterized amplified region，SCAR，mixed wasp competition testing