ABSTRACT
The objective of this study was to elucidate the chemical composition of essential oils from five Egyptian plants, namely Citrus reticulata, Schinus terebenthifolius, Mentha microphylla, Lantana camara and Eucalyptus camaldulensis, obtained by hydrodistillation and their biological activity on economic agricultural and public health pests. The isolated essential oils were tested for their larvicidal activity against Culex pipiens and fumigant toxicity against the adults of Culex pipiens, Musca domestica and Theba pisana. The antifeedant, topical, fumigant and residual toxicity of the isolated oils towards the larvae of Spodoptera littoralis were also examined. The isolated oils showed a strong larvicidal activity against the fourth instar larvae of C. pipiens in a concentration dependant manner. The oil of C. reticulata was the most effective among the tested oils followed by the oils of S. terebenthifolius and M. microphylla with LC50 values of 13.85, 20.75 and 22.42 mg/L, respectively. In a fumigant assay on the adults of C. pipiens, the isolated oils showed a potent toxic activity after 30 min of exposure. Eucalyptus camaldulensis oil exhibited the highest activity followed by M. microphylla oil with LC50 values of 0.96 and 2.47 microl/L. The results of the fumigant assay against the adults of M. domestica revealed that the oils were highly toxic after 1 and 24 hours of exposure with M. microcorphylla oil being the most effective. The larvicidal effects of the isolated oils against the third instar larvae of S. littoralis indicated that the assay method is an important factor for determining the toxicity of the isolated oils. The isolated oils showed a pronounced insecticidal potential in fumigant assay while they revealed a moderate to weak activity in both topical and residual assays. When tested for their antifeedant activity, the oils of S. terebenthifolius and L. camara were the most active among the tested oils at concentration of 1000 mg/L. Fumigant toxicity evaluated against the adult of T. pisana revealed that the oil of C. reticulata was the most toxic among the tested oils with LC50 value of 6.79 microl/L. The chemical composition of the isolated essential oils has been analyzed by gas chromatography-mass spectrometry [GC-MS]. Chemically, the major constituents of the oils belong to four main groups: oxygenated monoterpenes, monoterpene hydrocarbons, sesquiterpene hydrocarbons and oxygenated sesquiterpenes. The results obtained in this study suggest that, in addition to their other uses, the isolated oils can also serve as natural pest control agents