Essential oils

Definition

Hydrophobic volatile organic compound mixtures extracted from plant tissues—typically flowers, leaves, bark, or roots—that carry the characteristic fragrance or 'essence' of the source plant. In biological contexts, essential oils function as plant secondary metabolites with ecological roles including herbivore deterrence, antimicrobial defense, and pollinator attraction. In entomology and chemical ecology, they are studied as semiochemicals, botanical insecticides, and components of insect-plant interactions.

Etymology

From Latin 'essentialis' (of the essence) and 'oleum' (oil); 'essential' here refers to the oil containing the plant's characteristic essence or fragrance, not nutritional necessity.

Example

Monoterpenes in the essential oil of Mentha piperita (peppermint) repel aphids and serve as feeding deterrents, while the oil of Thymus vulgaris (thyme) containing thymol is used as a botanical acaricide against Varroa mites in honey bee colonies.

Synonyms

• volatile oils
• ethereal oils
• aetheroleum

Related Terms

• semiochemicals
• Allelochemicals
• botanical insecticides
• monoterpenes
• secondary metabolites
• Integrated Pest Management
• phytochemistry

Usage Notes

The term 'essential' does not imply dietary requirement (contrast with essential amino acids or essential fatty acids). In entomological literature, essential oils are distinguished from fixed oils by their volatility and are often analyzed via gas chromatography-mass spectrometry (GC-MS) to identify bioactive constituents. Efficacy as insecticides or repellents varies with chemical composition, concentration, and formulation; many essential oils show contact toxicity, fumigant action, or oviposition deterrence against stored-product pests and medical/veterinary arthropods.