The development of methods for efficiently capturing native parasitoids and their molecular identification has proved useful in basic and applied studies on parasitoids as biological control agents. In this study, we developed a method for capturing Cotesia vestalis, an important native parasitoid of the diamondback moth, Plutella xylostella, by periodically placing Komatsuna traps, consisting of potted Komatsuna (Brassica rapa) plants infested with P. xylostella larvae, in fields in Tsukuba, Ibaraki Prefecture, Japan from June to December in 2012. The traps were then transferred to our laboratory for collection of the parasitoids that later emerged from P. xylostella. We also developed specific PCR primers to identify C. vestalis. Our results reveal that a total of 62 parasitoids were captured using the traps during the experimental period, especially in June and July (n=58), and that all the parasitoids captured and then analyzed using the primers (n=58) were C. vestalis.