_____________________________________________________________________________________________________ *Corresponding author: E-mail: gitaarijaphet@gmail.com; Chemical Science International Journal 25(4): 1-6, 2018; Article no.CSIJ.46383 ISSN: 2456-706X (Past name: American Chemical Science Journal, Past ISSN: 2249-0205) Repellency Effects of Pelargonium citrosum and Rosmarinus officinalis Essential Oils against Housefly, Musca domestica L. (Diptera: Muscidae) Njiema Gitaari 1* , Patrick Kareru 1 and Mercy Githua 1 1 Department of Chemistry, School of Physical Sciences, College of Pure and Applied Sciences, Jomo Kenyatta University of Agriculture and Technology, P.O.Box 62000-00200 Nairobi, Kenya. Authors’ contributions This work was carried out in collaboration between all authors. All authors read and approved the final manuscript. Article Information DOI: 10.9734/CSJI/2018/46383 Editor(s): (1) Dr. Mazeyar Parvinzadeh Gashti, Department of Chemistry, Université Laval, 1045 Avenue of Medicine, Canada. Reviewers: (1) Jack D. Williams, Mercyhurst University, USA. (2) Aliva Patnaik, Sambalpur University, India. Complete Peer review History: http://www.sdiarticle3.com/review-history/46383 Received 02 November 2018 Accepted 15 January 2019 Published 22 January 2019 ABSTRACT Use of botanical environmentally friendly and biodegradable insect repellants as opposed to chemical insecticides is increasingly becoming important as an alternative method of insect control. Housefly (Musca domestica L.) has potential of transmitting pathogen causing diseases such as typhoid, cholera, bacillary dysentery, tuberculosis, anthrax, ophthalmia, and parasitic worms. The aim of this study was to evaluate the repellency of oil extracted from the leaves of Pelargonium citrosum and Rosmarinus officinalis. Extraction of essential oils was by hydro-distillation. Condensed oil extracts were collected in n-hexane and insect behavioral response tested using adult houseflies (Musca domestica L.). N, N-diethyl-m-toluamide (DEET) was used as the positive control and acetone as the negative control. The bioactive oil was then analyzed using GC-MS. The characteristic volatiles obtained from the two plants showed different compositions. P. citrosum oil comprised mainly of Linalool, Geraniol, m- Camphorene, 2-naphthalenemethanol-1,2,3,4,4a,5,6,7-octahydroalpha, Geranylangelate while R. officinalis comprised mainly of α-Pinene, , Eucalyptol, α-Terpinenol. Dose-response evaluations of these oils showed that R. officinalis oil was more repellent (LD 50 = 0.299 mg) than that of P. citrosum Original Research Article