海藻膠包埋左手香精油主要成分對桃蚜與小菜蛾的影響

Abstract

精油 (Essential oils, EOs) 為許多植物產生的次級代謝物，可能和對抗其天敵的防衛機制相關。精油的藥用價值已廣為人知，如芳香、治療用途、抗菌性能、昆蟲忌避和阻礙效果等，因此這些揮發性化合物在農業害蟲的管理應有很大的應用價值。精油是環境友善及在自然界中是可生物分解的，然而，因其可在短時間內經由蒸發、氧化和聚合作用等因素而快速降解而不受重視，所以迫切需要評估這些現存的問題。微膠囊化技術因其具有緩慢釋放效果常用於製藥工業，但在有害生物管理較少使用。本研究評估微膠囊化的左手香 (Plectranthus amboinicus (Lour.) Spreng.) 精油對於桃蚜 (Myzus persicae (Sulzer)) 與小菜蛾 (Plutella xylostella (Linnaeus)) 的防治效果。左手香精油主要的有效成分由14種合化合物組成，將其中三種含量最多的成分carvacrol, ρ-cymene 及β-caryophyllene以海藻酸鈉 (sodium alginate (SA)) 包埋，經氣相層析質譜儀 (Gas Chromatography-Mass Spectrophotometer, GC-MS) 及固相微萃取 (Solid Phase Microextraction, SPME) 分析0.5% SA 包埋的精油，ρ-cymene 在0~72小時內以高濃度釋放，β-caryophyllene 則相反；Carvacrol在各時段的釋放情形相同。膠囊化的效率測試結果顯示SA的濃度越高 (2%) 則效率越佳，但膠囊越大。再者，生物檢定結果顯示膠囊化的精油以劑量應變方式連續五天對桃蚜與小菜蛾具燻蒸毒性。然而，在開放空間下，膠囊化的精油對桃蚜的效果會因蒸氣會向多方向散逸而下降。反之，對小菜蛾的產卵阻礙檢定有不錯的效果，但對桃蚜的忌避檢定則不顯著。

Essential oils (EOs) are secondary metabolites produced by many plants which are found possibly crucial in defense mechanism against its natural enemies. They are also widely known for their medicinal, fragrant, therapeutic use, antimicrobial properties, insect repellent and deterrent effects. Thus, these volatile have great values towards the management of agricultural pest. Essential oils are environmental friendly and biodegradable in nature, however, essential oil has limited application due to rapid degradation over a short duration via vaporization, oxidation, polymerization, etc. This problem needs to be addressed. Microencapsulation technologies are commonly used in pharmaceutical industry because of its slow release effects, but less common in pest management. In this study, we evaluated the effect of encapsulated Plectranthus amboinicus (Lour.) Spreng essential oil towards Myzus persicae (Sulzer) and Plutella xylostella (Linnaeus). The active ingredients of Pl. amboinicus essential oils comprise about 14 complex compounds and three major components (carvacrol, ρ-cymene and β-caryophyllene) were encapsulated within sodium alginate (SA). Gas Chromatography-Mass Spectrophotometer (GCMS) analysis with Solid Phase Microextraction (SPME) adsorption founded that in 0.5% SA encapsulated oils, ρ-cymene was released in higher concentration at 0-72 hours whereas β-caryophyllene was the lowest. Carvacrol remains constant at all times. Encapsulation efficiency test displayed that the higher the concentration of SA (2%) the better is the encapsulating efficiency and the bigger is the size of the capsules. Bioassay results showed that encapsulated oils exhibits fumigant toxicity to M. persicae and P. xylostella for five consecutive days in a dose dependent manner. However, the effectiveness of encapsulated EOs towards M. persicae declined accordingly in open space that allows the fumes to escape at multiple directions. Oviposition deterrent assays with P. xylostella showed promising effects, while repellent assays were not significant towards M. persicae.