夏柑

Observations on the beneficial spider fauna were made between the insecticide-sprayed citrus groves and those receiving no insecticides around Hagi City, Yamaguchi Prefecture, West Honshu. Among the 66 spider species which are belonging to 16 families (Dictynidae, Uloboridae, Theridiidae, Theridiosomatidae, Micryphantidae, Agriopidae, Tetragnathidae, Pisauridae, Lycosidae, Oxyopidae, Agelenidae, Thomisidae, Salticidae, Clubionidae, Ctenidae and Gnaphosidae), Carrhotus detritus, Oxyopes sertatus, Araneus ejusmodi, Xysticus croceus, Philodromus subaureolus and Anahita fauna were more abundant. These species were richest in population from June to August or from September to November, but some species were most abundant in both seasons. Spiders were more numerous in the citrus groves receiving no sprays than in the insecticide-sprayed ones. Number of spider species was more abundant on the trees than on the undergrowth in the citrus groves with no sprays. On the contrary, in the citrus groves receiving insecticide-sprays the spiders were more numerous on the undergrowth than on the trees. This fact indicates that the effect of insecticides is much heavier on the spider population on the citrus trees than that on the undergrowth in the citrus groves.