三種臺灣產植物之萃取物對埃及斑蚊幼蟲的殺蟲活性

Abstract

登革熱一直是臺灣重要的公共衛生問題，此病已在近數十年來爆發過多次疫情。病媒蚊防治能夠防止或減緩登革熱疫情擴散，而使用合成殺蟲劑的化學防治是常用的防治手段。然而，過度使用合成殺蟲劑導致了害蟲抗藥性、危害非目標生物、長期汙染等問題。取自植物的殺蟲化學物質被認為是良好的化學防治藥劑替代品，因為藉由其複雜的作用機制、對人畜可能較為安全、可生物分解等特性能彌補合成殺蟲劑的問題。本研究目標為測試茵陳蒿(Artemisia capillaris)、棕葉狗尾草(Setaria palmifolia)、血桐(Macaranga tanarius)的萃取物對登革熱病媒蚊埃及斑蚊(Aedes aegypti)幼蟲的毒性。本研究室先前的研究顯示這些植物的萃取物對臺灣蛺蠓(Forcipomyia taiwana)具有忌避效果，但是其對蚊科的效果尚未被探討過。萃取物由這些植物的葉片經過冷凍、磨粉、以己烷和乙酸乙酯萃取而成，並在實驗室條件下，以不同的濃度測試其對埃及斑蚊幼蟲的殺蟲效果。測試結果顯示僅有茵陳蒿的己烷萃取物能作為有效的蚊蟲幼蟲殺蟲劑，其能夠快速擊暈幼蟲，且其在24與48小時內對埃及斑蚊幼蟲的半數致死濃度分別為187.60 ppm (v/v)與128.31 ppm。以氣相層析質譜儀分析各萃取物的化學成分的結果也顯示，和其他殺蟲效果較弱的植物萃取物相比，茵陳蒿己烷萃取物含有最多種被指出具殺蟲活性的化學物質。本研究的延伸方向包含測試化學協同作用的存在與否、探究殺蟲的作用機制、開發可實地應用的蚊蟲幼蟲殺蟲劑劑型。本研究也能對從植物中找尋殺蟲劑的生物探勘做出貢獻。

Dengue is a major public health concern in Taiwan, with multiple outbreaks in recent decades. Mosquito vector control is an effective way of preventing or mitigating the spread of the disease, and chemical control with synthetic insecticides is a common practice. Overuse of synthetic insecticides had led to problems such as resistance, non-target effects, and long-term pollution. Insecticidal chemicals derived from plants are considered good alternative options for chemical control agents due to their complex modes of action, potentially better safety to humans and domestic animals, and biodegradability. This study aimed to test the larvicidal effects of leaf extracts of capillary wormwood (Artemisia capillaris), palmgrass (Setaria palmifolia), and parasol leaf tree (Macaranga tanarius) against dengue vector yellow fever mosquito (Aedes aegypti). A previous study in our laboratory suggested that extracts from these plants have repellency effects against biting midges (Forcipomyia taiwana), but their effects against mosquitoes were yet to be explored. The plant leaves were frozen, ground into powder, and extracted with hexane and ethyl acetate. These extracts were tested in laboratory assays against larval Aedes aegypti at different concentrations. Only A. capillaris hexane extract was found to be an effective larvicide, causing fast knockdown and having an LC50 of 187.60 ppm (v/v) at 24 hours of exposure and 128.31 ppm at 48 hours of exposure. Gas-chromatography mass-spectrometry (GC-MS) determined chemical compositions of the tested plant extracts found that, compared to other less effective extracts, A. capillaris hexane extract contains the most chemicals reported to be insecticidal. This study may be further extended by checking for synergistic effects, exploring the modes of action, and developing mosquito larvicide formulations for field use, and the study can contribute to the bioprospecting for pesticides in plant-derived chemicals.