EFFICACY OF THE ESSENTIAL OILS OF AFRICAN BLUE BASIL (Ocimum kilimandscharicum GUERKE) AS A PYRETHRUM SYNERGIST

Abstract

Concern on quality and safety of life in managing pests has shifted steadily from the use of conventional chemicals towards alternative botanical insecticides that are target-specific, biodegradable and environmentally safe. The history of insecticidal synergists originated with attempts to enhance the potency of pyrethrins. This discovery initiated the use of insecticide synergists, piperonylbutoxide (PBO), which is obtained from Safrole a main component of sassafras. Ocimum kilimandscharicum of the family Lamiaceae, commonly known as African Blue Basil and ‘okita’ in native language, is a perennial, under shrub with simple ovate-oblong leaves. The essential oil of kilimandscharicum has carminative, stimulant, antipyretic, anti-fungal and anti-bacterial properties. Literature review has revealed that the chemical composition of the essential oil has several economic importance, among them increases potency of pyrethrum. The study was to investigate the synergism of pyrethrins with essential oils from O. kilimandscharicum. Specific objectives were to determine the activity of pyrethrins and the crude extracts (essential oil of O. kilimandscharicum) on 4th instar larvae and adult of Anopheles gambiae. Also to compare the efficacy of pyrethrins combined with essential oils against conventional pyrethrum synergist; Piperonyl butoxide (PBO). In light of this communication, this article presents essential oil composition from the leaves of O. kilimandscharicum, collected from the Kipkaren in Nandi County, Kenya, possessed an active ingredient that could be used as pyrethrum synergist. In this study, essential oils from O. kilimandscharicum leaves were extracted by hydro-distillation using Clevenger type apparatus for 4 hours. Crude extracts were used with pyrethrins to conduct bioassays for larvicidal activity against 4th instar larvae and adult of An. gambiae. Mortalities were recorded after 1, 3, 6, 9, 12 and 24 hour’s exposure. Bioassay data was evaluated by regression and probit analysis and used to determine the lethal doses (LC50 and LC90) for the synergist mixtures. The results showed that LC50 and LC90 values for O. kilimandscharicum with pyrethrins were 0.00167 and 0.0076mg/ml respectively. The components of the essential oils of O. kilimandscharicum was separated and identified by GC-MS. The analysis resulted to nineteen compounds in which the most efficacious was most probably methyleugenol. The findings of this research could enable investigation of the active compound against An. gambiae and further exploration for large scale production (synthesis) of the synergists for commercial application. Since biological products are biodegradable as opposed to convectional pyrethrum synergist, piperonylbutoxide (PBO) currently being used by the Pyrethrum Board of Kenya.