Callistemon citrinus (Myrtaceae) methanolic leaf extract: a potent mosquitocidal agent for controlling dengue vector mosquito Aedes aegypti (Diptera: Culicidae)

Abstract

Mosquitoes are the carriers of severe and well-known illnesses such as malaria, arboviral encephalitis, dengue, chikungunya and yellow fever, which cause significant morbidity and mortality in humans and domestic animals around the world. For many decades chemical insecticides are widely used to control mosquitoes. Mosquitoes have developed resistance against these chemical insecticides and also adversely affected the environment. There is an imperative demand to search novel eco-friendly substitutes which are more effective, safe and economical. Plant extracts with proven insecticidal properties are an alternate to these insecticides. The present study was aimed to investigate phytochemicals of the methanolic extract of C. citrinus. Bioassay test are carried out using the world health organisation standard method, for testing the efficacy of methanolic leaf extract of C. citrinus on Ae. aegypti at different stages of development viz I, II, III, IV instars and pupae and mortality was observed after 24 hrs exposure. Young larvae were found to be relatively more susceptible then the older ones. During the larvicidal bioassay with methanolic leaf extract of C. citrinus the fourth instar larvae of Ae. aegypti were monitored carefully for behavioural modifications. Behavioural observations of the methanolic leaf extract treated larvae revealed excitation and restlessness with persistent and aggressive anal biting behaviour indicating the probable effect of the extract on the neuromuscular system of larvae. Microscopic observations of the dead larvae showed shrunken internal membrane of anal papillae. The larvae of Ae. aegypti subjected to methanolic leaf extract treatment exhibited a variety of malformations during the course of their development. The current results were considered promising to proceed in studying the bioactive plants which represent an environmentally sound alternative for the synthetic insecticides.