露地ネギ圃場における土着カブリダニ類（ダニ目：カブリダニ科）の発生生態 (Japanese)

We investigated the occurrence of phytoseiid mites, as indigenous natural enemies of Thrips tabaciLindeman, in winter-harvested Welsh onion fields in Chiba Prefecture, Japan. Periodic surveys were carried out in fivefields, and six species of phytoseiid mites were captured. We assumed the dominant species was Gynaeseius liturivorus（Ehara）, because we captured this species in 8 fields during temporary surveys of 17 fields. Gynaeseius liturivoruspopulations were higher during October to December in winter-harvested Welsh onion fields receiving lower applicationsof agrochemicals than conventionally controlled fields. Adult female densities were significantly higher on the insidesof leaf folds than on other surface areas of the Welsh onions; all stages of G. liturivorus were frequently observedat peak abundance on the insides of the leaf folds. These results suggest that the insides of Welsh onion leaf folds providea suitable habitat for G. liturivorus. We identified their predatory potential against T. tabaci in the laboratory（adultfemales consumed 1.1±0.4 adults or 5.3±1.9 2nd instar larvae per day at 22°C with a 12L:12D photoperiod）, andobserved suppression of thrips in the fields at peak abundance of G. liturivorus. However, development of enhancedtechniques for insectary plants and evaluation of agrochemical effects on G. liturivorus are needed in order to sustainhigher mite densities, because the control of thrips by mites was not sustainable in this study. [ABSTRACT FROM AUTHOR]

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