10.22376/ijpbs.2019.10.1.p1-12 Volume 13 Issue 1 January - March Mosquitoes have an important role in spreading the deadly diseases such as malaria, Japanese encephalitis, dengue and filariasis etc. Malaria is the most vulnerable public health problem of present time. Malaria is caused by malarial parasite lessThan i greaterThan plasmodium falciparum lessThan /i greaterThan and is one of the leading causes of human morbidity and mortality from infectious disease, predominantly in tropical and sub-tropical countries. Chemicals involved in insect communication are called Semiochemicals. Semiochemicals are organic compounds used by insects to convey specific chemical messages that modify behaviour or physiology. Semiochemicals are used as fastest growing materials due to their unique physical, chemical and biological properties. Hexadecanoic acid is a novel semiochemical which was not fully evaluated against the malarial vector lessThan i greaterThan Anopheles stephensi. lessThan /i greaterThan The aim and objective of the present study was to evaluate the bio-efficacy of Hexadecanoic acid against the malarial vector lessThan i greaterThan Anopheles stephensi lessThan /i greaterThan . Hexadecanoic acid was screened to assess Larvicidal, efficacy against the 3 lessThan sup greaterThan rd lessThan /sup greaterThan instar larvae and pupicidal activity at different concentrations ranging from 5-45 ppm against malarial vector lessThan i greaterThan Anopheles stephensi lessThan /i greaterThan after 24h .The repellent activity was also assessed against lessThan i greaterThan An. stephensi lessThan /i greaterThan at three different concentrations viz., 1.0, 2.0 and 4.0 mg/cm lessThan sup greaterThan 2 lessThan /sup greaterThan of treatment after 24h under the laboratory conditions. The compound was found to be effective against the mosquito. The LC lessThan sub greaterThan 50 lessThan /sub greaterThan and LC lessThan sub greaterThan 90 lessThan /sub greaterThan values for larvicidal bio-assay were 16.309, 28.624 ppm and for pupicidal bio-assay 30.311, 42.776 ppm respectively. Hexadecanoic acid also showed higher repellency with the increase in concentration. The highest repellency was observed at a concentration of 4.0mg/cm lessThan sup greaterThan 2 lessThan /sup greaterThan provided 100 percent protection up to 120 min against lessThan i greaterThan An. stephensi. lessThan /i greaterThan Hence the results revealed that the Hexadecanoic acid is potential compound for controlling the vector mosquito. Junaid Hassan and Arulsamy Jebanesan Semio chemical, Hexadecanoic Acid, An. Stephensi, Malaria 37-43