水生之黃緣螢幼蟲的化學防禦：翻縮腺之顯微結構、分泌物成分與對不同掠食者的效能

Chemical Defense of Aquatic Larvae of the Firefly (Aquatica ficta): Microanatomy of Eversible Organs, Chemicals of Glandular Secretion, and Effectiveness to Different Predators

陳君玳(Chun-Tai Chen) ； 吳加雄(Chia-Hsiung Wu) ； 鄭明倫(Ming-Luen Jeng) ； 楊平世(Ping-Shih Yang)

《台灣昆蟲》 32卷1期 (2012/03) Pp. 41-57

https://doi.org/10.6661/TESFE.2012003

摘要

本研究報導黃緣螢（Aquatica ficta（Olivier））的水棲幼蟲的化學防禦。幼蟲受到接觸性的刺激後，會蜷縮身體，並伸出分叉狀之翻縮腺。翻縮腺共10對，分佈於中、後胸及腹部第1～8節之體側氣管腮與背板間。第五齡幼蟲之翻縮腺外部表面具有眾多的花苞狀小突起，端部有對稱或放射狀排列的小刺，可分為3～6辦四型，小突起內部無其他構造；翻縮腺內部表面具有為半圓球狀的腔室，內具粒線體，以小管和外表面的花苞狀小突起相連，應為防禦物質之分泌腺體。質化觀察黃緣螢幼蟲的化學防禦是否對不同的共域掠食者都有效，發現對於魚類的效果最好，實驗的泥鰍吞食幼蟲後會將其無傷地吐出，最終拒絕取食；細蟌科的水蠆攫捕黃緣螢幼蟲後並未完全取食，但已使幼蟲死亡；貪食沼蝦則不僅攫捕黃緣螢幼蟲，並以第一螯肢剪開幼蟲表皮，不斷扭轉幼蟲，最終將幼蟲取食殆盡。利用氣相層析質譜儀分析翻縮腺之分泌物質成分，共發現12種化合物，有3種為未知，其餘為單萜類衍生物，其中terpinolene、L-(-)-verbenone、(-)-sabinene等為主要成份，相對含量9.81～20.87％；以市售之terpinolene，以不同劑量混入市售魚飼料後倒入2％洋菜基內調製為0.0425、0.425與4.25％三種濃度的人工食餌，餵食泥鰍與貪食沼蝦，測試terpinolene對不同掠食者的忌避性。泥鰍及貪食沼蝦對三種terpinolene濃度之人工食餌塊呈現不同程度的排拒性，濃度越高，排拒性越強；對泥鰍之忌避率為30～95％，對貪食沼蝦為20～80％。生物活性測試證實黃緣螢幼蟲翻縮腺所分泌的terpinolene對天敵的確具有忌避效果。

關鍵字

黃緣螢 ； 幼蟲化學防禦 ； 掠食者 ； 生物活性檢定

並列摘要

The larval chemical defenses of the Yellow-rimmed Aquatic Firefly, Aquatica ficta (Olivier), were studied. The larvae, when simulated by touch, would curl up their body into a ball and stretch their forked-shape eversible organs accompanied with a pine- odor. Ten pairs of eversible organs are located bilaterally on meso- and metathoracies, as well as on the first 8 abdominal segments, just above the abdominal tracheal gills. The external surface of the eversible organs of the fifth-instar larvae bears many bud-like micro-protuberances, each with 3-6 spines radially arranged on the top. No significant ultrastructure was found within the micro-protuberance. On the internal surface of the eversible organs there are many hemispherical structures, which have rich mitochondria inside, each of which is connected to a micro-protuberance on the external surface with a tubule. These hemispherical structures are believed to be the secretion glands. Four kinds of predators were used to test the effectiveness of the chemical defense of the firefly larvae. The larvae successfully defended against attacks by Dojo Loaches (Misgurnus anguillicaudatus), and were unharmed ejected out of the mouth of the loach. The larvae were hunted and partially consumed by damselfly naiads (of Coenagrionidae). Freshwater prawns (Palaemonidae, Macrobrachium lar) were able to mechanically neutralize the chemical defense of the firefly larvae and consumed the whole larval body. This suggests that the larval chemical defense is less effective against invertebrate predators, although the predator may eventually abandon the dead prey. Using gas chromatography-mass spectrometry (GC-MS), we identified nine chemical components, plus another three unknown substances, that were extracted from the larval eversible organs. The identified components are largely monoterpene compounds, such as terpinolene, L-(-)-verbenone, (-)-sabinene, limonene, and γ- terpinene, etc. Among them terpinolene has the richest content (20.87%) and was chosen for a bioassay test. Agar-based pellets containing commercial fish food and three different concentrations of terpinolene (0.0425, 0.425 and 4.25%) were fed to the Dojo loaches and freshwater prawns (Macrobrachium lar) to determine their deterrence. Pellets of each of the three concentrations showed a deterrent effect of different degrees to the subject predators in relation to non-terpinolened pellets. The higher the concentration, the stronger the deterrence. Dojo loaches showed a 30-95% deterrent efficiency. Freshwater prawns were less sensitive to terpinolene than loaches, and showed a 20-80% deterrent efficiency. The terpinolene secreted by the larval eversible organs was confirmed to be a repellent against predators.

並列關鍵字

Aquatica ficta ； larvae chemical defense ； predators ； terpinolene ； bioassay