Studies on Mosquitocidal and biological activity of endemic plants of Nilgiris Hills against filarial vector, Culex quinquefasciatus (Say) (Insecta: Diptera: Culicidae)

The methanol leaf extracts of Glochidion neilgherrense, Cinnamomum wightii and Leucas linifolia are highly toxic even at low doses proven to be useful for larvicidal, pupicidal and adulticidal activity against Culex quinquefasciatus. The extraction of Glochidion neilgherrense, Cinnamomum wightii and Leucas linifolia are dose dependent and the mortality of the larvae increases as the doses of the sample were increased. Among all the instars, the fourth instar larvae were less susceptible to the plant extracts than first instar larvae. The mortality caused by some neural and muscular disturbance by the presence of variety of active compounds such as cytotoxic diterperiods, lactones and flavonoids in the plants. It was observed that the increase in concentration of extracts increased the potential activity of biocides against Culex quinquefasciatus. The decrease in egg hatchability was found to be dose dependent. There was increase in the larval-pupal duration, developmental duration, decrease in fecundity and egg hatchability, biting deterrency, in our study. The extract showed ovipositional deterrence and effective repellence against Culex quinquefasciatus at different concentration, with the observation on that maximal egg were laid in lower concentration of the extract and control. In oviposition deterrent and gravid mortality assay, the OAI values also indicated that the gravid and oviposited females were repelled by extracts and the reduced oviposition was due to the greater mortality of adults before they oviposited, caused by treatment of plant extract which contained of variety of active compounds. All the concentration of plant extracts hared promising mosquito repellency properties when tested against the adult mosquitoes of Culex quinquefasciatus. In the biting deterrency results, increasing in the concentration of plant extracts from 1% to 4% was found to increase the biting deterrency percentage.