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蟲生線蟲（Steinernema taiwanensis strain T39）對斜紋夜蛾及甜菜夜蛾（鱗翅目：夜蛾科）致病力之比較
Pathogenicity of the Entomopathogenic Nematode, Steinernema taiwanensis Strain T39, Against Two Noctuids, Spodoptera litura and Spodoptera exigua (Lepidoptera: Noctuidae)
摘要
本試驗以生物檢定研究台灣本地產蟲生線蟲(Steinernema taiwanensis strain T39)對斜紋夜蛾(Spodoptera litura Fabricius)及甜菜夜蛾(Spodoptera exigua Hübner)之致病力。溫度對致病力之測試結果顯示，雖因昆蟲種類不同導致其表現略有差異，然而S. taiwanensis strain T39適宜溫度範圍介於25～35°C，在20°C以下則無死亡率發生。不同濃度之S. taiwanensis strain T39懸浮液接種斜紋夜蛾幼蟲，結果顯示五齡或六齡幼蟲對含防腐劑或未含防腐劑飼料處理組間之最終寄主死亡率均無顯著差異，然在飼料內未含防腐劑者所得之LT_(50)皆較含防腐劑組為低，且線蟲對六齡幼蟲之致病力較五齡幼蟲為佳。接種濃度20 IJs/mL時，取食未含防腐劑或含防腐劑飼料之斜紋夜蛾五齡幼蟲，其半致死時間(LT_(50))分別為37.9及39.9 h；接種濃度為25 IJs/mL者之六齡幼蟲LT_(50)則為27.0及28.4 h。以甜菜夜蛾供測，則在同樣處理下接種濃度20 IJs/mL之五齡幼蟲之最終死亡率與斜紋夜蛾之試驗結果間無顯著差異，然其LT_(50)為27.2 h明顯較短，顯示S. taiwanensis strain T39對甜菜夜蛾之致死速率較斜紋夜蛾為快。綜合上述試驗結果證實，S. taiwanensis strain T39對斜紋夜蛾及甜菜夜蛾具有殺蟲效力。
並列摘要
The pathogenicity of the entomopathogenic nematode, Steinernema taiwanensis strain T39, isolated from Taiwan was determined using bioassays against two noctuids, Spodoptera litura and Spodoptera exigua. When incubated both noctuid larvae after the inoculation with the nematode suspension at different temperatures, the results showed that, although mortalities varied within host species, the optimum temperatures for S. taiwanensis infection were 25-30°C. However, the inoculated larvae of both insect species did not exhibit any mortality at temperatures below 20°C. Inoculation of S. litura larvae with three concentrations of S. taiwanensis did not reveal any significant difference in cumulative mortalities among various treatments; however, the median lethal time (LT_(50)) values of fifth and sixth instar larvae fed on the diets without antiseptics were shorter than those on the antiseptic-containing diets. The LT_(50) values of fifth instar larvae fed on the diets with or without antiseptics after inoculation with S. taiwanensis at 20 IJs/mL were 37.9 and 39.9 h, respectively, whereas those of sixth instar larvae inoculated with the nematode at 25 IJs/mL were 27.0 and 28.4 h, respectively. In the other assay with S. exigua fed on diets without antiseptics, the cumulative mortalities caused by inoculation with S. taiwanensis at 20 IJs/mL were not significantly different; however, the LT_(50) value was ca. 27.2 h, which was shorter than that of S. litura, indicating that S. taiwanensis can kill S. exigua faster than S. litura. Therefore, it is suggested that S. taiwanensis is pathogenic to the larvae of both noctuid species.