以益達胺注射刺桐樹防治刺桐釉小蜂

Abstract

刺桐屬 (Erythrina) 植物多為生長於熱帶地區之耐乾旱樹種，許多地區都以刺桐做為行道路樹，另外也有許多具紀念性質的刺桐老樹佇立於鄉間鄰里。自從新種外來入侵的造癭昆蟲刺桐釉小蜂 Quadrastichus erythrinae Kim，入侵台灣後，對原生刺桐屬植物造成嚴重危害，至今疫情已蔓延全台。植食性造癭昆蟲幼蟲期完全在癭組織中生活，以噴灑的化學藥劑防治難見成效，而珍貴的刺桐老樹在藥劑施用上更有一定的難度。因此，本研究利用防治林木害蟲的藥劑樹幹注射法，將系統性藥劑益達胺 (Imidacloprid) 注射入輸導組織中，利用其水分輸導作用而將藥劑移行至葉上癭組織中，毒殺刺桐釉小蜂。初期試驗以樹徑大小做為施用劑量標準，結果發現針劑注射 3 週後，小樹實驗組 (樹徑 < 20 cm) 每克蟲癭葉片中刺桐釉小蜂羽化率顯著低於對照組，而較大樹徑 (樹徑 > 20 cm) 的植株則需長達 1 年後才能看出成效。因此在老樹的部分則採每多 5 cm 樹徑注射 5 ml 藥劑的方式進行注射。由於老樹分枝較多，若以主幹作為估算藥劑之標準效果不盡理想，故以主要樹幹分枝數量、及各分枝粗細作為針劑數量的判定標準。藥劑注射 1 個月後，老樹上刺桐釉小蜂的蟲癭數量大為降低，藥劑注射後危害期數亦大幅降低，並與注射前呈顯著差異。隨著樹勢的回復，樹幹注射的孔道於 3 ∼ 4 個月後逐漸癒合。利用液像層析分析的結果顯示，藥劑注射後益達胺的移行作用隨著時間迅速傳導，使全株葉片的益達胺含量達到刺桐釉小蜂的致死劑量。而隨老葉脫落後，新抽葉片益達胺含量都較低，樣樹卻仍可維持極低的刺桐釉小蜂危害期數，可能與低劑量藥劑造成釉小蜂發育受阻有密切相關。本研究除了確立以樹幹注射法防治刺桐釉小蜂及藥劑移行的時間外，成果亦可提供未來防治大型木本植物植食性造癭害蟲之技術參考。

Coral tree (Erythrina) is one of drought-tolerant plants which commonly grown in tropical regions. In many areas, coral trees are planted as street trees or shade trees. In addition, there are many elder coral trees are also commemorative for residents in some rural neighborhoods. But the native coral tree species in Taiwan get serious damage since the invasion of a new galling arthropod pest, erythrina eulophid wasp (Quadrastichus erythrinae). So far this galling wasp has spread across Taiwan. The Q. erythrinae spends entire larva stage in the gall tissues, and this characteristic makes it become difficult to kill with traditional chemical control methods. Therefore, in this study, trunk injection method, which is commonly used for forestry pest control, was employed to inject imidacloprid into gall tissues directly. For quantifying the necessary insection into a tree, finding out the correlation between tree diameters and imidacloprid dosage is the priority task to investige. Experiment result of Q. erythrinae emerge rate shows significant difference between imidacloprid treated group and untreated one, but it shows no difference when tree diameter is larger than 20 cm until one year later. According to the preliminary result, the number of major branches as a standard to estimate the suitable imidacloprid dosage will be used for the application of trunk injection on elder trees. The quantity of imidacloprid is based on tree’s diameter (when every additional 5 cm diameter is increased in branches, then we will inject additional 5 ml imidacloiprid). And picture-monitoring results show that damage stage drop down significantly in one month after injection. The injecting pits were also healed four months later. High performance liquid chromatography analysis presents a unique transition mechanism that imidacloprid can transport to the upper layer and reach lethal dosage in just three weeks. Even though the imidacloprid dosage in leaves drops down in several weeks, the low concentration still can affect the growth of Q. erythrinae. This study does not only present an effect evaluation of trunk injection control method for controlling Q. erythrinae, but also provides an useful reference for controlling other galling phytophagous pests.