Seasonal abundance of Scirtothrips dorsalis (Thysanoptera: Thripidae) in citrus orchards related with surrounding host plants in Jeju, South Korea

The damage of citrus by Scirtothrips dorsalis was increased after 2007 year in Jeju, but it is not clear for characteristic of seasonal abundance. This study was conducted to investigate the host plants of S. dorsalis distributed around citrus orchards and its seasonal abundance in relation to those plants. The host plants of S. dorsalis surrounding citrus orchards were found on 32 families 54 species: 39 species were woody plants and 15 species were herbaceous ones. The host plants which related to the occurrence of 1st generation of S. dorsalis were Lonicera japonica, Clematis apiifolia, Hedera rhombea, and Viburnum awabuki. The occurrence of 1st generation of S. dorsalis was estimated that the overwintered female adults laid eggs into those plants from late March to early April and the new adults emerged from late April to late May. The host plants which were associated with fruit damage of citrus were Mallotus japonicus, Camellia japonica and the creeping plants such as Clematis apiifolia, Paederia scandens and Cayratia japonica. The peak periods of adult density of S. dorsalis caught on yellow-color sticky trap placed on the citrus tree coincided with on the edge of the citrus orchard. S. dorsalis might pass 7 generations in Jeju and the 3rd generation (from early to late of July) and 5th generation (from middle August to early September) was directly related to the damage of citrus fruit. The density of S. dorsalis was depending on the number of new growing shoots of host plants. This result showed that the adults of S. dorsalis immigrated to the citrus synchronized with emerging from other suitable host plants surrounding the orchards.