左手香精油對埃及斑蚊及熱帶家蚊幼蟲差異毒性機制研究

Abstract

蚊蟲是許多疾病的傳播媒介，包含瘧疾、登革熱和茲卡病毒感染症。蚊蟲的防治策略通常依賴合成殺蟲劑，但合成殺蟲劑常產生抗藥性，也有環境污染問題，因此，必須尋找嶄新的防治策略，而精油是一種環境友善防治害蟲很好的替代方案。實驗室先前研究顯示相較於埃及斑蚊幼蟲，熱帶家蚊幼蟲對左手香精油較敏感，而β-石竹烯有可能是造成左手香精油對埃及斑蚊及熱帶家蚊幼蟲毒性不同的主要成分。本研究的目的為探討左手香精油對埃及斑蚊及熱帶家蚊幼蟲毒性差異機制。細胞色素P450 (CYP) 及穀胱甘肽S-轉移酶 (GST) 在蚊蟲對抗殺蟲劑的過程中扮演重要角色，實驗結果顯示埃及斑蚊幼蟲GSTe2及CYP6M family的表現量均較熱帶家蚊幼蟲高，尤其GSTe2的表現量於埃及斑蚊幼蟲更顯著高於於熱帶家蚊幼蟲。胡椒基丁醚 (細胞色素P450抑制劑) 及1-氟-2,4-二硝基苯 (GSH抑制劑) 均可提升埃及斑蚊及熱帶家蚊幼蟲對β-石竹烯的敏感性，但以1-氟-2,4-二硝基苯對埃及斑蚊幼蟲的影響較對熱帶家蚊幼蟲顯著。顯示GSH的含量與埃及斑蚊及熱帶家蚊幼蟲對β-石竹烯的敏感度有關，為造成左手香精油對埃及斑蚊及熱帶家蚊幼蟲毒性差異的主要原因。

Mosquitoes are vectors for many diseases, including malaria, dengue fever, and Zika virus infection. Strategies for mosquito control mainly rely on synthetic insecticides which always results in insecticide resistance and environmental pollution. Therefore, development of eco-friendly strategies for vector control is urgent and essential oil (EO) is an alternative method for pest control. Previous studies have shown larva of Culex quinquefasciatus was more sensitive than that of Aedes aegypti to Plectranthus amboinicus EOs. β-caryophyllene might be the major component responsible for the differential toxicity of P. amboinicus EOs, as indicated by the significant differences in its LC50 values toward both mosquitoes. This thesis aims to delineate the mechanisms responsible for the differential toxicity of P. amboinicus EOs toward both mosquito larvae. The currrent results showed that the relative expression levels of GSTe2 (as well as GSH contents) and CYP6M family in Ae. aegypti larvae were higher than that in Cx. quinquefasciatus larvae. In particular, the difference of GSTe2 is more significant than that of CYP6M family in both mosquito larvae. Though both piperonyl butoxide (PBO, an inhibitor of cytochrome P450) and 1-fluoro-2,4-dinitrobenzene (DNFB, a GSH-depleting agents) treatment potentiated the sensitivity of Ae. aegypti and Cx. quinquefasciatus larvae to β-caryophyllene, DNFB imposed more significant effect in Ae. aegypti larvae than to Cx. quinquefasciatus larvae. These results suggested both GSH contents and GSTs level are the major factors contributing to the different sensitivity of Ae. aegypti and Cx. quinquefasciatus to β-caryophyllene and the mechanism responsible for the differential toxicity of P. amboinicus essential oils toward Aedes and Culex mosquito larvae.