Damages by Tyrophagus spp. (Acari: Acaridae) on horticultural crops were newly observed in recent years especially in organic culture greenhouses in Korea. The crops damaged by the mite species were Spinacia oleracea L. (spinach), Cucumis sativus (cucumber), and Phalaenopsis schilleriana (orchid). The spinach inner leaf growth was halted affected by the feeding of Tyrophagus similis at the early stage of the shoot emergence. The young leaves of the spinach bud had small holes and the leaves were deformed as they grew up. The surface of young cucumber fruits became shiny and soft at the early damage stage and the damaged surfaces became corky as the plants grew up. The mite from cucumber was identified as Tyrophagus neiswanderi Johnston & Bruce. In phalaenopsis orchid, the flower buds became yellow and dropped and the lower side of the leaves had white spots. The damages were caused by Tyrophagus putrescentiae.

A mite damage was observed in spinach (Spinacia oleracea L.) under organic culture greenhouses. The mite was identified as Tyrophagus similis Volgin, 1949. It was very difficult for the farmers to diagnose the mite damage because of its tiny size about 0.5 nm in length. And the symptom was not clear at the early growth stage of the spinach because the mite mainly attack the very young leaves. In this study, we first report the spinach damages by T. similis in Korea. Informations on the mite morphology and the spinach damage symptoms are provided for the diagnosis.