Seasonal occurrence of japanagromyza tokunagai (Sasakawa) (Diptera:Agromyzidae) on Cymbidium kanran 'Makino' (Orchidaceae) in Jeju Island, Republic of Korea and prevention of infestation by the fly

摘要

Cymbidium kanran 'Makino' - commonly known as cold-growing cymbidium -blooms between November and January in the Republic of Korea. Its only known natural habitat in the country is on Jeju Island. A strict law has been implemented to protect both thespecies and its natural habitat. In 2011, we investigated serious damage to the orchid peduncles that resulted in the failure of most orchids in the habitat to bloom. In the present study, we aimed to identify an insect pest and its damage to the orchids, and to formulate preventive measures to protect the orchid from that pest. Surveys were conducted once per month in the protected habitat from November 2011 to December 2012. We collected damaged flower stocks and ovaries (or seedpods), surveyed otherorchid species in and around the site, and identified the insect pest and parasitoids collected during the surveys. The damage to the peduncles and ovaries of C. kanran was inflicted by the larvae of Japanagromyza tokunagai (Sasakawa) of the family Agromyzidae. The fly is multivoltine; it infests Cymbidium goeringii from November to June, Cephalanthera falcata and Cymbidium erecta from June to August, and C. kanran from August to November. In other places, the fly also infests the ovaries of Oreorchis coreana and Cypripedium macranthos. We found two hymenopteran parasitoids of the fly during the surveys: Pediobius metallicus {Eulophidae) - a predominant parasitoid - and Sphegigaster sp. cf. brevicornis (Pteromalidae). As a preventative measure, the cold-growing cymbidiums were covered with fine mesh net cages to prevent the fly from infesting the flower stalks from August, when the peduncles start to grow. The net cages reduced the level of fly infestation to 20% (19 damaged out of 95 peduncles).