10.22376/ijpbs.2019.10.1.p1-12 Volume 10 Issue 4 2019 (October-December) Malaria is a mosquito-transmitted disease, which is one of the most prevalent diseases in the tropical world. It is caused by the malarial parasite, lessThan i greaterThan Plasmodium falciparum lessThan /i greaterThan which is transmitted to humans through the bite of the lessThan i greaterThan Anopheles lessThan /i greaterThan mosquito. Lemon grass oil ( lessThan i greaterThan Cymbopogon citratus) lessThan /i greaterThan based nanoemulsion has been developed for large field breeding mosquitoes like lessThan i greaterThan An. stephensi lessThan /i greaterThan . Lemon grass oil nanoemulsion was formulated in different ratios comprising of lemon grass oil, surfactants and water by using ultrasonication. The ratio of lemon grass oil (90%) water (2.5%) and surfactants Tween-20 (2.5%) was found to be stable. The lemon grass oil nanoemulsion was characterized by dynamic light scattering and the PDI (polydispersity index) of the nanoemulsion was found to be 0.02. Lemon grass oil nanoemulsion was screened for its efficacy against lessThan i greaterThan An. stephensi lessThan /i greaterThan . The bioassay showed an LC lessThan sub greaterThan 50 lessThan /sub greaterThan 3.30 ppm and LC lessThan sub greaterThan 90 lessThan /sub greaterThan 8.70 ppm, respectively after 24 h of exposure. The nanoemulsion was diluted in distilled water at various concentrations. The concentration expressed as lessThan i greaterThan Cymbopogon citratus lessThan /i greaterThan essential oil content on aqueous media. A botanical nanoformulation has been developed which is biodegradable, environment and user friendly approaches for the vector control programme. MAYAKRISHNAN VIJAY, ARULSAMY JEBANESAN AND JAYAPAL SUBRAMANIAM Nanoemulsion, Cymbopogon citratus, Anopheles stephensi, Larvicidal activity, Ultrasonication, Polydispersity. 155-161