Abstract
Aedes aegypti is a vector of emerging and neglected diseases, such as dengue, chikungunya, and Zika. Helicteres velutina, known as “pitó” in Brazil, is traditionally used as an insect repellent, and several studies have demonstrated its larvicidal activity. The aim of this study was to investigate this species and evaluate its potential ovicidal, pupicidal, adulticidal, and repellent activity. The viability of the eggs was evaluated using different concentrations of the test substances for 25 days. The hexane fraction killed 72.7% of the eggs, while dichloromethane killed 67.7%. The survival of the pupae and adults was verified after 72 h and 48 h, respectively. The LC50 for the hexane and dichloromethane fractions was 0.12 mg/mL and 8.85 mg/mL for pupae, 8.01 mg/mL and 0.74 mg/mL for adults (tarsal test), and 0.05 mg/mL and 0.23 mg/mL for adults (body test), respectively. Repellency was assessed for 240 min using neonatal Wistar rats on a Y-tube olfactometer. The hexane fraction attracted mosquitoes to the test chamber, while the dichloromethane fraction had a repellent action. The 7,4’-di-O-methyl-8-O-sulfate flavone provides greater repellency, and this finding is similar to the results of the in silico studies that have shown the potential of this substance against adult mosquitoes. This suggests that 7,4’-di-O-methyl-8-O-sulfate flavone may be one of the substances present in the extract from aerial parts of H. velutina that is responsible for the repellent activity mentioned in traditional medicine. These findings provide a better understanding of the insecticidal and repellent activity of the extract, fraction, and compounds isolated from H. velutina against Ae. aegypti, thereby revealing its potential in the development of a more effective botanical insecticide.
Highlights
Emerging infections, including dengue, Zika, and chikungunya, caused by arboviruses that are transmitted by Aedes aegypti L. are of great concern to the World Health Organization (Leta et al, 2018; Rojas-Pinzón et al, 2018)
Our results revealed that the hexane fraction obtained from the crude ethanolic extract (CEE) of aerial parts of H. velutina, exhibited significantly higher activity against eggs, pupae, and adult mosquitoes, suggesting that components such as triterpenes, steroids, fatty acids, and pheophytins isolated from this fraction could possess activity against these phases of the vector’s life cycle
While testing the repellent activity, we found that the hexane fraction attracted mosquitoes to the test chamber and that the CEE was less active than the dichloromethane fraction at all the analyzed concentrations and intervals, leading to the proposition that the compounds existing in the dichloromethane fraction would be responsible for the repellent action
Summary
Emerging infections, including dengue, Zika, and chikungunya, caused by arboviruses that are transmitted by Aedes aegypti L. are of great concern to the World Health Organization (Leta et al, 2018; Rojas-Pinzón et al, 2018). 2.5 billion people live in high-risk areas, especially in the tropical and subtropical regions of the world, where temperature and humidity promote the proliferation of such vectors (Kraemer et al, 2015; Reegan et al, 2014). Mosquito control is an effective alternative for preventing the spread of these diseases, and management programs focus as much on the control of the immature vectors (egg, larvae, and pupae) as on adult mosquitoes (Chellappandian et al, 2018; Wang et al, 2018). Prolonged use of these compounds leads to ecological imbalance and consequent harmful effects on non-target organisms in addition to the development of resistance. The search for natural alternatives that are safe, selective, economically viable, and biodegradable is important (Ravindran et al, 2012; Vivekanandhan et al, 2018)
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