水生黃緣螢幼蟲之化學防禦

Abstract

黃緣螢 (Luciola ficta Olivier) 幼蟲遇刺激干擾後，會蜷曲體節、伸出分叉狀之翻縮腺，並伴隨難聞之「松香」氣味以避敵。翻縮腺共有 10 對，分佈於黃緣螢中、後胸及腹部第 1~8 節，位於體側之氣管腮與背板間。五齡幼蟲之翻縮腺外部表面佈滿不規則形之花狀突起，有 3~6 辦四型，突起內未發現其餘構造；內部為周圍凹陷之半圓球體，具粒線體，應為防禦物質之分泌腺體；突起及分泌腺體藉由管狀通道連結，應為輸送分泌物質之用。 捕食者捕食黃緣螢情形各有不同，細蟌科 (Coenagrionidae) 水蠆取食黃緣螢幼蟲之機率僅 16％，造成幼蟲受傷或死亡，但不會將幼蟲全部食入；泥鰍 (Misgurnus anguillicaudatus) 於試驗時間內會不斷攻擊黃緣螢幼蟲，但取食後則立即吐出，而幼蟲則無受傷或死亡情形發生；長臂蝦科 (Palaemonidae) 具翻轉並撥出黃緣螢幼蟲內物質之行為，將黃緣螢幼蟲取食殆盡。黃緣螢幼蟲對於不同類別之捕食者之忌避效果雖有不同，但可推測其防禦機制應使用味覺防禦大過於視覺防禦。 利用氣相層析質譜儀分析翻縮腺之分泌物質成分，共測得 82 個吸收峰，去除雜質與含量過低之吸收峰後，僅剩 12 個吸收峰，共佔所有分析物質中 85％，其中 9 個吸收峰為已知物質。由於此分析所測得之吸收峰單純且結果穩定，可判定主要成份於黃緣螢幼蟲防禦中扮演重要角色。 主要成份由高至低依序為 Terpinolene (相對含量 20.87％，滯留時間 17.35 分鐘)、L - (-) - Verbenone (相對含量 12.23％，滯留時間 21.13 分鐘)、(-) - Sabinene (相對含量 9.31％，滯留時間 11.07 分鐘)、Limonene (相對含量 1.28％，滯留時間 14.20 分鐘)、γ - Terpinene (相對含量 1.22％，滯留時間 15.82 分鐘) ……等等。黃緣螢幼蟲之分泌物質大多為單萜類衍生物，此類物質已確定具有忌避、抗蟲、抗菌……等效果，目前已可以人工合成方式大量生產。 將市售 Terpinolene 調製為0.0425％、0.425％、4.25％……等三個不同濃度，混入市售魚飼料後倒入 2％洋菜基內，以未添加 Terpinolene 之洋菜基為控制組，餵食捕食者。三種濃度所製作之洋菜基飼料塊，對於泥鰍及長臂蝦皆有顯著忌避作用。 三種由低到高不同濃度的 Terpinolene 對於泥鰍之忌避率由 30％∼95％不等，對於長臂蝦之忌避率則由 20％∼80％不等；由此忌避率可得知，長臂蝦對於 Terpinolene 之耐受性較高，與生物忌避試驗結果相符。

Aquatic firefly larvae, Luciola ficta Olivier will curl body and stretch forked-shape eversible organs after simulating. In the meantime, “pine oil” smell will be spread. Ten pairs of eversible organs distribute on meso- and metathorax, as well as the abdomen 1-8, above the tracheal gills on the pleural. The external structure of eversible organs of the fifth instar larvae is densely covered with flower-shaped protuberances. There are 3-6 petals on the protuberances, and no additional structure within protuberances. There are several hemi-spheres with hollow surrounding on the inner surface of eversible organs, which have mitochondrion inside. It should be the secretion gland that for defense. The protuberance and secretion gland connected with tube structure, should be the channel of secretion. There are several conditions between different predators attack L. ficta larvae. It shows 16％ possibility that Coenagrionidae nymph prey on L. ficta larvae, and make firefly larvae injure or die. In that situation, Coenagrionidae nymph do not consume whole body of L. ficta larvae. In Loach (Misgurnus anguillicaudatus) experiment, they will attack L. ficta larvae several times within the experimental time, and then spit it out immediately. In the meantime, the firefly larvae will not be hurt. On the contrary, shrimp (Palaemonidae) will rotate L. ficta larvae and push aside their internal body part, then consume the larvae. There are different deterrent effects on different kinds of predators, the defense mechanism of L. ficta larvae should be the sense of taste, rather than the visual defense. Using gas chromatography-Mass spectrometry (GC - MS) detect the secretion chemicals of larvae, and get 82 peaks. Ignore impurities and the peaks less than 0.05％, only get 12 peaks, possess about 85％ area. There are well known chemicals on 9 peaks within the analysis results. The peaks of results are simple and stable, the main components of secretion should play an important role in the chemical defense of L. ficta larvae. The main components of eversible organs ranked from high to low are Terpinolene (relative area = 20.87％, RT = 17.35 min), L - (-) - Verbenone (relative area = 12.23％, RT = 21.13 min), (-) - Sabinene (relative area = 9.31％, RT = 11.07 min), Limonene (relative area = 1.28％, RT = 14.20 min), and γ - Terpinene (relative area = 1.22％, RT = 15.82 min), and so on. Most of the secretions of L. ficta are monoterpene derivatives. These derivatives are confirmed that have deterrent effects, resistance of insects, and antibacterial properties. It can be produce by artificial synthesis in great quantity. Add terpinolene concentration in 3 concentration, 0.0425％、0.425％、4.25％, into commercial fish food and mix with 2% agar. The control food without terpinolene, then feed predators with different concentration. There are obviously deterrent efficiency in Misgurnus anguillicaudatus and palaemonidae in different concentration. 3 terpinolene concentration ranked from low to high have 30％- 95％ deterrent efficiency of loach, and 20％- 80％ deterrent efficiency of shrimp. From the results, the tolerance of shrimp is higher than loach, fit in with the results of deterrent experiment of L. ficta.