Abstract
Helicteres velutina K. Schum (Sterculiaceae), a member of Malvaceae sensu lato, is a Brazilian endemic plant that has been used by the indigenous tribe Pankarare as an insect repellent. A previous study has reported the isolation of terpenoids, flavonoids and pheophytins, in addition to the larvicidal activity of crude H. velutina extracts derived from the aerial components (leaves, branches/twigs, and flowers). The present study reports the biomonitoring of the effects of fractions and isolated compounds derived from H. velutina against A. aegypti fourth instar larvae. A crude ethanol extract was submitted to liquid–liquid extraction with hexane, dichloromethane, ethyl acetate and n-butanol to obtain their respective fractions. Larvicidal evaluations of the fractions were performed, and the hexane and dichloromethane fractions exhibited greater activities than the other fractions, with LC50 (50% lethal concentration) values of 3.88 and 5.80 mg/mL, respectively. The phytochemical study of these fractions resulted in the isolation and identification of 17 compounds. The molecules were subjected to a virtual screening protocol, and five molecules presented potential larvicidal activity after analyses of their applicability domains. When molecular docking was analysed, only three of these compounds showed an ability to bind with sterol carrier protein-2 (1PZ4), a protein found in the larval intestine. The compounds tiliroside and 7,4′-di-O-methyl-8-O-sulphate flavone showed in vitro larvicidal activity, with LC50 values of 0.275 mg/mL after 72 h and 0.182 mg/mL after 24 h of exposure, respectively. This is the first study to demonstrate the larvicidal activity of sulphated flavonoids against A. aegypti. Our results showed that the presence of the OSO3H group attached to C-8 of the flavonoid was crucial to the larvicidal activity. This research supports the traditional use of H. velutina as an alternative insecticide for the control of A. aegypti, which is a vector for severe arboviruses, such as dengue and chikungunya.
Highlights
Aedes aegypti (Diptera: Culicidae) is the primary vector for emerging and often neglected human-transmitted diseases, such as dengue, yellow fever and, more recently, the chikungunya and zika viruses [1]
Based on the previously reported larvicidal potential of H. velutina extracts [16], here, we report here a biomonitoring study to identify which compounds in the extracts are responsible for the larvicidal activity [17,18]
Previous studies have demonstrated the larvicidal activity of crude ethanolic extracts (CEEs) derived from the stems, roots, and aerial components of H. velutina, with LC50 (50% lethal concentration) values of 138.896 mg/mL, 171.683 mg/mL and 2.983 mg/mL, respectively [15,16]
Summary
Aedes aegypti (Diptera: Culicidae) is the primary vector for emerging and often neglected human-transmitted diseases, such as dengue, yellow fever and, more recently, the chikungunya and zika viruses [1]. A. aegypti is a vector for Fever Valley Rift, a serious emerging zoonotic disease that affects cattle [2]. The primary method for the prevention of arbovirus spread is controlling the vector, especially during the adult and larval stages [3,4]. The non-selective ingestion of particles by larvae makes the use of larvicides based on digestive action a potential method for vector control [5]. Substances extracted from plants have been shown to display important larvicidal effects [6]. Previous studies have reported the activities of plant extracts on the immune systems of mosquitoes
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