Abstract
Background: Aedes aegypti L.; one of the most important insect vectors in the world; transmits several diseases of concern; Zika, yellow fever, Chikungunya, dengue and dengue haemorrhagic fever. Despite multifarious problems on humans, non-targets and environment; caused by synthetic chemical insecticides; these are still the prime and preferred control measures against dengue vector. Alternative control strategies using eco-friendly and bio-degradable plant products are being explored. Objective: The present study investigates the toxic potential of the hexane extract of the leaf and stem of Achyranthes aspera against Ae. aegypti. Methods: The larvicidal potential of extracts was evaluated against dengue larvae as per WHO protocol. Subsequent concentration and time-dependent studies assessed their effects on the larval midgut histo-architecture using microtomy techniques. Results: Larvicidal bioassays with A. aspera extracts revealed their appreciable larvicidal potential. Hexane extract of the leaf resulted in respective LC30, LC50 and LC90 values of 67, 83 and 140 ppm while exposure to hexane extract of the stem showed respective values of 55, 68 and 115 ppm. Extract-exposed larvae at various lethal levels exhibited significant damage, shrinkage, distortion and vacuolization of gut tissues and peritrophic membrane. The disintegration of epithelial cells and cytoplasmic organelles evidenced stomach poison potential of the extracts. The extent of toxicity and damage was concentration and time-dependent; the stem extract imparted more deleterious effects as compared to the leaf extract. Conclusion: Present findings suggest the utilization of A. aspera as an alternate control strategy against Ae. aegypti; though further studies against non-targets are needed to ascertain its use in the fields.
Highlights
Aedes aegypti L. is a worldwide disease vector, transmitting a number of diseases; dengue, Chikungunya, dengue hemorrhagic fever, yellow fever and Zika
The mortality of early fourth instars of Ae. aegypti when exposed to graded series of hexane extract of the leaf and stem of A. aspera for 24 h are presented in Table 1 and Fig. 1
Exposure of early fourth instars of Ae. aegypti with hexane extract of the leaf of A. aspera resulted in respective LC30, lethal concentrations causing 50% mortality (LC50) and LC90 values of 67, 83 and 140 ppm while larval exposure to hexane extract of the stem showed respective values of 55, 68 and 115 ppm (Table 2)
Summary
Aedes aegypti L. is a worldwide disease vector, transmitting a number of diseases; dengue, Chikungunya, dengue hemorrhagic fever, yellow fever and Zika. World Health Organization has recorded almost 30-fold increase in the dengue incidence since last 50 years causing health risks to almost half of the world population. In India, Union health ministry recorded a total of 99,913 dengue and 27,553 Chikungunya cases in 2015. The increasing number of reported cases transmitted by Ae. aegypti year after year has made this mosquito one of the most serious disease vectors. Aedes aegypti L.; one of the most important insect vectors in the world; transmits several diseases of concern; Zika, yellow fever, Chikungunya, dengue and dengue haemorrhagic fever. Despite multifarious problems on humans, non-targets and environment; caused by synthetic chemical insecticides; these are still the prime and preferred control measures against dengue vector. Alternative control strategies using eco-friendly and bio-degradable plant products are being explored
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