Repellency and Antimicrobial Effects of Pelargonium citrosum and Rosmarinus officinalis L Plant Extracts

Abstract

Use of botanical environmentally friendly and biodegradable insect repellents 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 which causes diseases such as parasitic worms, anthrax, tuberculosis, bacillary dysentery, cholera and typhoid. Human diseases can be treated and prevented by essential oils with biological properties which have been derived from aromatic plants. In this study antimicrobial activities and housefly repellence of P. citrosum and R. officinalis was evaluated separately and in products formulated from the extracts. Extraction of essential oils was by hydro-distillation. Condensed oil extracts were collected in n-hexane and insect behavioural response tested using adult houseflies (Musca domestica L.). N,N-diethyl-m-toluamide (DEET) acted as the positive control with acetone acting as the negative control. The bioactive oil was then analysed using GC-MS. The characteristic volatiles obtained from the two oils 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 (LD50 = 0.299 mg) was more repellent than that of P. citrosum (LD50 = 0.445 mg). The Disk diffusion method was used to carry out the antimicrobial activities of the R. officinallis and P. citrosum. The outcomes showed that the P. citrosum essential oils had antimicrobial activity against Candida albicans, Escherichia coli and Bacillus subtilis at a low concentration of 0.5 % v/v and that the activity was concentration dependent. R. officinalis essential oils, on the other hand, exhibited active antimicrobial properties against Candida albicans, Staphylococcus aureus, Escherichia coli and Pseudomonus aeruginosa. The study showed that P. citrosum was more effective than gentamicin and nitrofuractoin drugs against Staphylococcus aureus at a higher concentration of 6 % v/v. Oil extracts from R. officinalis also illustrated similar trends and were similar to the positive controls against the tested microbes. These results provide scientific justification for traditional use of R. officinalis oil and Pelargonium citrosum essential oils for the control of housefly and other common insects in the household.