植物遭受植食者取食後會被誘導產生防禦反應，以降低害蟲族群數量。這些反應包括藉由直接誘導防禦降低植食者生長表現，或是間接防禦反應吸引植食者的天敵以降低害蟲數量。而植食者密度減低、發育減緩、品質下降等情形，也會影響天敵的生長。茉莉花酸(JA)為一植物荷爾蒙，在許多植物遭受植食者攻擊所誘導的防禦路徑中扮演重要角色。前人研究指出外源施加甲基茉莉花酸(MeJA)可以誘導植物產生防禦反應，抵抗後來的植食者。本試驗為瞭解大豆施用甲基茉莉花酸後，對斜紋夜蛾(Spodoptera litura)以及其天敵馬尼拉小繭蜂(Snellenius manilae)的影響。本試驗包含三部分，第一部分為觀察大豆施用甲基茉莉花酸後，對斜紋夜蛾生長表現的影響，並測量植物防禦物質的變化。第二部分為評估取食甲基茉莉花酸施用葉片之斜紋夜蛾幼蟲對馬尼拉小繭蜂生長表現的影響。第三部分為觀察馬尼拉小繭蜂對施用甲基茉莉花酸之大豆的行為偏好表現。試驗結果發現大豆受甲基茉莉花酸誘導後對三齡斜紋夜蛾幼蟲生長產生負面影響，造成斜紋夜蛾幼蟲的食物消化率(AD)降低，雖然消化食物轉換率(ECD)會上升，但整體而言相對生長速率(RGR)約降低20%。對馬尼拉小繭蜂的生長表現除了幼蟲期延長約0.5天之外，在繭重以及成蟲壽命上皆無顯著差異。大豆葉片經甲基茉莉花酸誘導後48小時對馬尼拉小繭蜂具吸引力。本試驗發現大豆經MeJA誘導後會產生直接防禦反應，對斜紋夜蛾生長表現產生負面影響，此外也會產生間接防禦反應吸引馬尼拉小繭蜂。 Plants would produce induced defense responses when they are damaged by herbivores, and decrease populations of herbivores. Those responses that including direct defense which can decrease performance of herbivores or indirect defense which can attract the natural enemy that against pests. In addition, lower performance of herbivore would also affect performance of natural enemy. Jasmonic acid (JA) is a plant hormone, play an important role in defense pathway induced by herbivores in many plants. Previous studies have indicated that exogenous methyl jasmonic acid (MeJA) in plants can induce defense responses against herbivores. The objective of this study is to understand the effect of MeJA treated soybean on performance of the armyworm (Spdoptera litura) and its parasitoid wasp Snellenius manilae. Three main experiments are included in this study. First, we used soybean leaves that treated with MeJA and fed to armyworm and observe the performance of armyworm. Secondly, we observed the performance of wasp which parasitized the armyworm which fed soybean leaves treated with MeJA. In the final study, we observed the attraction of wasp to soybean leaves treated with MeJA. Results of this study suggests that soybean treated with MeJA would induced defense response to decrease the performance of armyworm decrease the approximate digestibility (AD) and relative growth rate (RGR). MeJA would increase the larvae stage of the Snellenius manilae, but have no significant different in cocoon weights and longevity. In addition, soybean leaves treated with MeJA after 48 hours demonstrated the attracting ability.