Seasonal and spatial population change of Tetranychus urticae (Acari: Tetranychidae) on strawberry of plastic greenhouse under the forcing cultural system

Seasonal and spatial population change of T. urticae was investigated to understand their dispersion attributes on strawberry of plastic greenhouse under the forcing cultural system. Different strawberry varieties ¨C Maehyang, Sulhyang, Keumhyang, Akihime, and Seonhong ¨C were planted on a rotary field (5.2 m width and 28 m length) by the split plot design method. Each plot was divided into six or seven sampling blocks (0.4 x 1.0 m each). The investigation was conducted by examining six randomly selected leaflets per block from 13 October, 2006 to 27 April, 2007 and from 2 October, 2007 to 22 April, 2008 at one week intervals. The data were transformed by ln (x+1). Repeated-measures data were analyzed by MANOVA. We could not find T. urticae during first experimental season. T. urticae population increased when Aphis gossypii (Hemiptera: Aphididae) was vanished by parasitoid and daily average temperature was over 14°æ during second experimental season. The distribution pattern of T. urticae was clumped and it diffused along the row from arrival point. There was little seasonal coincidence between A. gossypii and T. urticae during second season. The population sizes of T. urticae was different among varieties (F=16.86, p=0.0001), time (F=211.68, p=0.0001) and time x varieties (F=7.62, p=0.0001) during second experimental season.