AbstractDiplogasteroidessp., a cryptic population ofD. haslacheri, andParasitorhabditis terebranuswere reported from the frass ofMonochamus alternatusgalleries in deadPinus thunbergiifor the first time in Korea. Females and males are morphologically characterized and their linked DNA barcodes (18S-rRNA, 28S-rRNA, ITS-rRNA and COI) supplied. Females and males of the two species from Korea conform to the original species descriptions from Europe and the USA, with variations in a few details in morphometrics. Specifically,Diplogasteroidessp. is morphologically very similar toD. haslacheri. However, it cannot be designated asD. haslacheridue to the existence of cryptic species complex within thehaslacherigroup (D. haslacheri,D. asiaticus, D. nix, D. andrassyi, andD. carinthiacus), a condition requiring hybridization studies to test species identity within the group. Based on analysis of COI sequences, differences among these cryptic species are evident. Thus, in addition to hybridization tests, the COI might be a powerful DNA barcoding marker for the precise identification of these cryptic species within the genus. Additionally, this is the first molecular characterization ofP. terebranus, and the species is herein recorded for the first time outside its type locality.