Abstract
Viral diseases transmitted by the female Aedes aegypti L. are considered a major public health problem. The aerial parts of Helicteres velutina K. Schum (Sterculiaceae) have demonstrated potential insecticidal and larvicidal activity against this vector. The objective of this research was to investigate the mechanisms of action involved in the larvicidal activity of this species. The cytotoxicity activity of H. velutina fractions and compounds of crude ethanolic extract of the aerial parts of this species was assessed by using fluorescence microscopy and propidium iodide staining. In addition, the production of nitric oxide (NO) and hemocyte recruitment were checked after different periods of exposure. The fluorescence microscopy revealed an increasing in larvae cell necrosis for the dichloromethane fraction, 7,4′-di-O-methyl-8-O-sulphate flavone and hexane fraction (15.4, 11.0, and 7.0%, respectively). The tiliroside did not show necrotic cells, which showed the same result as that seen in the negative control. The NO concentration in hemolymph after 24 h exposure was significantly greater for the dichloromethane fraction and the 7,4′-di-O-methyl-8-O-sulphate flavone (123.8 and 56.2 µM, respectively) when compared to the hexane fraction and tiliroside (10.8 and 8.3 µM, respectively). The presence of plasmocytes only in the dichloromethane fraction and 7,4′-di-O-methyl-8-O-sulphate flavone treatments suggest that these would be the hemocytes responsible for the highest NO production, acting as a defense agent. Our results showed that the larvicidal activity developed by H. velutina compounds is related to its hemocyte necrotizing activity and alteration in NO production.
Highlights
Aedes aegypti L. (Diptera: Culicidae) is a major vector for viruses that threaten human health, such as dengue, chikungunya, and Zika
In order to continue the ongoing work with H. velutina against A. aegypti larvae, this study investigates the possible mechanisms of action involved in the larvicidal activity of fractions and isolated substances [12,13] by analyzing in vitro cytotoxicity and nitric oxide (NO) production
In this study, using the needed concentration to kill all exposed larvae, it was registered that the dichloromethane fraction of crude ethanolic extract of aerial parts of H. velutina (10.0 mg/mL)
Summary
Aedes aegypti L. (Diptera: Culicidae) is a major vector for viruses that threaten human health, such as dengue, chikungunya, and Zika. 2.5 billion people live in high-risk areas, especially in tropical and subtropical regions of the world where temperature and humidity promote their proliferation [1,2,3]. Efficient vaccines against these arboviruses have not yet been developed, making vector control the main form of preventing these diseases. Several natural products are considered promising for use as insecticides, repellents, or larvicides, due their biodegradability, efficiency, and low cost [4,5]. According to Faraldo et al (2005), the larvae possess an extremely efficient immune system that is an excellent model for studying insect defense mechanisms [6]. In contrast to the complexity of the vertebrate immune system, the relative simplicity of the invertebrate immune system makes it a potentially sensitive and accessible means of monitoring the effects of environmental contaminants and the complex interactions that affect host resistance [7]
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