Abstract
Aedes aegypti is responsible for the transmission of dengue, a disease that infects millions of people each year. Although essential oils are well recognized as sources of compounds with repellent and larvicidal activities against the dengue mosquito, much less is known about their oviposition deterrent effects. Commiphora leptophloeos, a tree native to South America, has important pharmacological properties, but the chemical profile and applicability of its essential oil in controlling the spread of the dengue mosquito have not been investigated. The aim of this study was to determine the composition of C. leptophloeos leaf oil and to evaluate its larvicidal and oviposition deterrent effects against A. aegypti. Fifty-five components of the essential oil were detected by gas chromatography (GC)—mass spectrometry, with α-phellandrene (26.3%), (E)-caryophyllene (18.0%) and β-phellandrene (12.9%) identified as the major constituents. Bioassays showed that the oil exhibited strong oviposition deterrent effects against A. aegypti at concentrations between 25 and 100 ppm, and possessed good larvicidal activity (LC50 = 99.4 ppm). Analysis of the oil by GC coupled with electroantennographic detection established that seven constituents could trigger antennal depolarization in A. aegypti gravid females. Two of these components, namely (E)-caryophyllene and α-humulene, were present in substantial proportions in the oil, and oviposition deterrence assays confirmed that both were significantly active at concentrations equivalent to those present in the oil. It is concluded that these sesquiterpenes are responsible, at least in part, for the deterrent effect of the oil. The oviposition deterrent activity of the leaf oil of C. leptophloeos is one of the most potent reported so far, suggesting that it could represent an interesting alternative to synthetic insecticides. The results of this study highlight the importance of integrating chemical and electrophysiological methods for screening natural compounds for their potential in combating vectors of insect-borne diseases.
Highlights
Aedes aegypti (Linnaeus) is a known vector of various viruses including those responsible for yellow fever, dengue fever and chikungunya [1]
In comparison with respective controls, the presence of C. leptophloeos leaf oil in concentrations of 25, 50 or 100 ppm induced a reduction of more than 50% in the oviposition of A. aegypti gravid females (Fig 1)
A number of studies of essential oils from species of Commiphora have shown that the chemical profiles of leaf oil within the genus are highly diverse [54,55,56,57,58,59,60,61,62]
Summary
Aedes aegypti (Linnaeus) is a known vector of various viruses including those responsible for yellow fever, dengue fever and chikungunya [1]. According to the most recent estimates of the World Health Organization some 50 to 100 million people are infected with dengue each year [2], and this is alarming because no effective vaccine has been developed so far [3]. Control of the mosquito vector remains the principal method available through which to limit the dissemination of the dengue virus. Aedes aegypti is a diurnal mosquito that is well adapted to urban areas, in tropical regions where sanitation is poor [4]. Effective control of the mosquito became dependant on the limited number of synthetic insecticides available [11] and constrained by the deleterious effects of such compounds on the ecosystem and on human health [12]
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