Camptomyia is a genus of gall midges belonging to subfamily Porricondilinae, with 42 species known from the palaearctic region. In November 2007, serious damages of the Shiitake mushroom logs were reported in many shiitake farms from the middle part of South Korea. Rearing the adults in laboratory, a Camptomyia species was recognized as the major species causing damages on shiitake. Colonies of maggots were observed, feeding the mycelium of shiitake mushroom and the phloem of oak timbers, disturbing the mushroom fruit body formation. The morphology of the larvae and adult of this Camptomyia heterobia. is illustrated with the description of the damage symptom.