Bioassay of Larvicidal Efficacy of Selected Plant Extracts Against Mosquito Larvae Anopheles Culicifacies and Aedes Aegypti L.

ABSTRACT: Mosquitoes act as a vector and are the most significant nuisance for spreading many diseases, viz. malaria, dengue and filariasis encephalitis. The extensive use of chemical insecticides to control these vector-borne diseases causes adverse environmental impacts, pest resurgence, vertebrate toxicity, and physiological resistance to vectors. The present research work was undertaken to study the efficacy of ethanolic extracts of commonly available plants, viz. Paederia foetida, Murraya koenigii, Zingiber officinale and Allium sativum against the larvae of the mosquitos, Aedes aegypti and Anopheles culicifacies at different sub-lethal concentrations (50 mg, 100 mg, 150 mg per 100 ml of water) for 1 hour, 10 hours, 24 hours, 48 hours, 72 hours and one week of exposure. The study was based on the behavioural changes, mortality rate and larval development following standard technique. The phytochemical screening for these plants was carried out following standard methods. The investigation results showed abnormal changes in the behaviour, such as hyperactive wriggling movement in the initial period. In contrast, sluggish and motionless movements were also observed in the later days of exposure associated with an upward mouth posture on the water surface indicative of the moribund condition.  The impairment of the larval development and attainment of fly size was also noted in that they respond variedly to the different plant extracts in a dose and time-dependent manner. The mortality rates in these two mosquito larvae with respect to these plant extracts have also recorded an increasing trend, i.e., A. sativum> P. foetida> Z. officinale> M. koenigii.  Keywords: Mosquito Larvae, Plant Extracts, Larvicidal Activity, Phytochemicals.