An Area-wide Occurrence of the Two-Spotted Spider Mite, Tetranychus urticae (Acari: Tetanychidae), Observed in Wax Gourd (Benincasa hispida) Greenhouses on Miyako Island, Okinawa, in 2009, and Subsequent Disappearance of the Spider Mites

Abstract

Although Tetranychus urticae Koch (green form) has rarely been found on the southwestern region of Okinawa (the Sakishima Islands), we found an unexpected simultaneous occurrence of this species in 2009 in wax gourd greenhouses on one of the islands (Miyako Island). In that year, T. urticae occurred in 43% of wax gourd fields among the surveyed fields. In 2010, however, the frequency of occurrence naturally decreased; the species was found in only 3% of the fields from January to May and later become not found. These results have important implications for controlling spider mites on vegetable greenhouses in that area. Specifically, T. urticae can temporarily increase, but it cannot colonize the Sakishima Islands permanently due to some unknown biotic or abiotic factor(s). Neither the infestation frequency nor the species composition of other Tetanychus spider mites in the wax gourd greenhouses varied significantly between 2009 and 2010, suggesting that the occurrence of T. urticae did not affect the occurrence of other congeners.