Abstract
Purpose: To determine the larvicidal activity of the essential oil derived from Isodon japonicus var. glaucocalyx (Maxim.) H.W.Li (Labiatae) aerial parts at flowering stage against the larvae of Aedes aegypti L. Methods: The essential oil of I. japonicus var. glaucocalyx aerial parts was obtained by hydrodistillation and analyzed by gas chromatography (GC) and gas chromaotography-mas spectrometry (GC-MS). The activity of the essential oil was evaluated, using World Health Organization (WHO) procedures, against the fourth larvae of A. aegypti for 24 h, and larval mortality recorded at various essential oil concentrations ranging from 12.5 - 200 µg/mL. Results: A total of 34 components of the essential oil of I. japonicus var. glaucocalyx were identified. The principal compounds of the essential oil were thujone (9.65 %), morillol (8.14 %), caryophyllene oxide (7.68 %), β-caryophyllene (7.60 %), α-terpineol (7.22 %), 1,8-cineole (7.09 %), linalool (5.56 %), Z-caryophyllene (5.10 %) and γ-eudesmol (4.71 %). The essential oil exhibited larvicidal activity against A. aegypti with a median lethal concentration (LC 50 ) of 40.82 µg/mL. Conclusion: The findings indicate that the essential oil of I. japonicus var. glaucocalyx aerial parts has potentials for use in the control of A. aegypti larvae and may be useful in the search for newer, safer and more effective natural compounds for use as larvicides.
Highlights
Mosquitoes play an important role in the transmission of malaria, dengue fever, yellow fever, chikungunya, filariasis, several forms of encephalitis and filariasis as well as several diseases which are today among the greatest health problems in the world
Monoterpenoids represented 13 of the 34 compounds, corresponding to 41.27 % of the whole essential oil while 18 of the 34 constituents were sesquiterpenoids corresponding to 43.16 % of the essential oil of I. japonicus var. glaucocalyx aerial parts
The major compounds in the essential oil of I. japonicus var. glaucocalyx aerial parts collected from Gansu province, China were 2-ethoxy propane (15.49 %), 2-methyl hexane (8.06 %) and methyl salicylate (3.58 %) [21]
Summary
Mosquitoes play an important role in the transmission of malaria, dengue fever, yellow fever, chikungunya, filariasis, several forms of encephalitis and filariasis as well as several diseases which are today among the greatest health problems in the world. The yellow fever mosquito (Aedes aegypti L) and the Asian tiger mosquito (A. albopictus Skuse) and are two main species of mosquito responsible for dengue fever in China. The use of synthetic insecticides (organophosphates such as dichlorvos, temephos and fenthion) and insect growth regulators (such as diflubenzuron and methoprene) is the most widespread method for control of mosquito larvae [1]. Heavily repeated use of these synthetic insecticides has fostered several environmental and health concerns, including disruption of natural biological control systems, outbreaks of other insect species, widespread development of resistance and undesirable effects on non-target organism [2]. It is suggested that many essential oils and constituent compounds derived from various essential oils can exert toxic activity against mosquito species [3,4,5,6]
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