Monochamus alternatus (M. alternatus) and Monochamus saltuarius (M. saltuarius) are major vectors for Bursaphelenchus xylophilus in South Korea. When an adult, they are easily distinguishable by several morphological classification. However, it is difficult to identification between M. alternatus and M. saltuarius when they are larvae as they have very similar morphological characters. Thus, they are not easily distinguishable without expertise about Cerambycidae taxonomy. Furthermore, during epidemiological investigation, sometimes, adults or larvae would not be founded in death pine trees. For these reasons, in this experiment, we are able to identified between M. alternatus and M. saltuarius by mitochondrial 12S rRNA gene primers that are specific to 12S rRNA gene fragment of M. alternatus using larvae tissue and frass. Moreover, we had examined whether vectors that were already escaped from dead pine tree have Bursaphelenchus xylophilus or not by multiplex PCR using larva frass that was remained in dead pine tree.