Chemical composition and mosquito repellent activity of the essential oil of Plectranthus incanus link

Abstract

The chemical composition of the essential oil obtained from the leaves of Plectranthus incanus Link, with the yield of 0.6% (w/v), was analyzed by GC and GC/MS. A total of 16 constituents, representing 95.2% of the oil, were identified. The major components of the oil were fenchone (6.0%), piperitone oxide (32.4%), piperitenone (3.0%) and piperitenone oxide (41.5%). The repellent activity of the volatile oil at different concentrations was measured by the protection period against the bites of Anopheles stephensi and Culex fatigans. The tested oil had stronger repellent activity than citronella oil, which was used as a positive control. LC50 (30 min) for P. incanus oil against An. stephensi and C. fatigans were 23.8 and 19.6 ?l/L air, respectively, whereas LC50 of citronella oil were 31.7 and 31.0 ?l/L air. Thus, P. incanus may be regarded as a potential valuable source of chemicals that have strong mosquito repellent activity, and could be used for the preparation of mosquito repellent formulations.Hemijski sastav etarskog ulja izolovanog iz listova biljne vrste Plectranthus incanus Link, sa prinosom od 0,6% (v/m), analiziran je pomocu gasne hromatografije i gasne hromatografije sa masenom detekcijom (GC i GC/MS). Uspesno je identifikovano ukupno 16 jedinjenja, koja su sacinjavala 95,2% ulja. Glavni sastojci su bili fenhon (6,0%), piperiton oksid (32,4%), piperitenon (3,0%) i piperitenon oksid (41,5%). Testirano je odbojno dejstvo dobijenog ulja (pri razlicitim koncentracijama) prema komarcima, merenjem perioda zastite od ugriza Anopheles stephensi i Culex fatigans. Analizirano ulje pokazalo je jace odbojno dejstvo prema komarcima od "citronela" ulja, koje je korisceno kao pozitivna kontrola. Pored toga, dobijene LC50 vrednosti (merenje je vrseno nakon 30 minuta) za An. stephensi i C. fatigans su bile nize u slucaju P. incanus (23,8 i 19,6 ?l/L vazduha) u odnosu na "citronela" ulje (31,7 i 31,0 ?l/L vazduha). Prema tome, biljna vrsta P. incanus bi se mogla smatrati potencijalnim vrednim izvorom jedinjenja sa jakim odbojnim dejstvom prema komarcima, te bi se mogla koristiti za pripremu odgovarajucih zastitnih preparata.