Impact of Achyranthes aspera Leaf and Stem Extracts on the Survival, Morphology and Behaviour of an Indian Strain of Dengue Vector, Aedes aegypti L. (Diptera: Culicidae)

Abstract

Aedes aegypti; well-known vector associated with the transmission of dengue, chikungunya and yellow fever; has attracted substantial attention worldwide because of the alarming increase in disease statistics. Laboratory investigations were carried out to evaluate the impact of extracts; prepared from the stems and leaves of Achyranthes aspera; on the survival, behaviour and morphology of Ae. aegypti larvae. Healthy and disease-free parts of A. aspera extracted in hexane were screened for their larvicidal activity against early fourth instars of dengue vector in accordance with the WHO protocol. The investigations clearly established the larvicidal efficiency of both the extracts, though hexane stem extracts proved to be 0.82 fold more efficient than the leaf extracts. The bioassay resulted in LC50 value of 68.133 and 82.555 ppm, when larvae were exposed to the hexane stem and leaf extracts of A. aspera, respectively. On the other hand, at LC90 level, the hexane leaves extract proved to be 18% more efficient as compared to the hexane stem extract of A. aspera. Behavioural observations of the treated larvae revealed excitation and restlessness with persistent and aggressive anal biting behaviour indicating the probable effect of the extracts on the neuromuscular system of larvae. Microscopic observations of the dead larvae showed shrunken internal membrane of anal papillae and abnormally stretched body. Further the treated larvae of Ae. aegypti showed distorted alimentary canal with loss of pigmentation and partial or total cell destruction. Our results suggest the probable use of hexane extracts of A. aspera as an efficient and eco-friendly larvicide against Ae. aegypti. Further investigations are needed to identify the bioactive constituent and ascertain its effectiveness in the field conditions