Repellent, contact and fumigant activities of geranium (Pelargonium graveolens L.’Hér) essential oils against Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.)

Geranium ( Pelargonium graveolens ) is an economic plant in Egypt that can resist insect infections, which may be related to its oils. Three types of geranium essential oils (geranium oil, geranium absolute and geranium stripping oil) were extracted with three different methods (steam distillation, solvent extraction, and hydrodistillation respectively). The three types of crude essential oils, three natural components (linalool, citronellol, and geraniol), and synthetic counterparts of two of these components (linalool and citronellol) were evaluated against Tribolium castaneum and Rhyzopertha dominica adults using two bioassays evaluating their repellency and fumigation effects. The tree types of crude geranium essential oils were analysed by gas chromatography/mass spectrometry (GC-MS). Chromatographic analysis of the geranium essential oils demonstrated that citronellol is the main constituent, accounting 29.70, 31.80 and 18.30% of geranium oil, geranium stripping oil and geranium absolute, respectively. Geranium absolute had the highest repellent activity against T. castaneum . In contrast, geranium stripping oil had the greatest repellency against R. dominica . Furthermore, natural linalool had the strongest fumigant effect on T. castaneum among the oil components , while citronellol had the strongest effect on R. dominica , and the oil components had stronger fumigant effects than the crude geranium oils. The fumigation activity showed the same trend as repellency against the two tested insects. Based on the LC50, the oil components having a stronger effect than the crude geranium oils. Finally, T. castaneum was more tolerant than R. dominica to all tested materials. The method of extraction effects on the chemical composition of essential oils produced from the same plant, all tested crude essential oils and its components (natural and synthetic) can be used as safe pesticide alternatives for stored product insects, geranium stripping oil is a new crude oil can increase the national income instead of losing it in waste water.