A new species of the genus Eumerus (Diptera: Syrphidae) infesting roots of Campanulaceae crops in South Korea

•A syrphid, Eumerus platycodon Choi et Hong sp. nov. is described new species in the world.•This syrphid pest is damaged roots of Platycodon grandiflorum (balloon flower) and Adenophora triphylla var. japonica.•The neighbor-joining tree showed that Eumerus platycodon is low intraspecific genetic distances.•The matured larvae burrow into the soil and pupated during about 10 days.•There is occurred at least two generations per year.