Essential oils are concentrated extracts from plants, containing the potent aromatic compounds that give the plant its characteristic scent. These volatile substances are the plant’s natural defense and communication system. Some essential oils effectively repel pests, while others can actually attract them. Understanding the difference is key to using these natural products effectively for insect management.
Why Certain Essential Oils Attract Insects
The primary reason certain essential oils act as attractants is that their chemical profile mimics the volatile organic compounds plants release to signal to insects. Many floral or fruity essential oils contain compounds that smell like a food source or a host plant to specific insects. Plants rely on these scents to draw in beneficial insects, like pollinators.
For instance, the terpene alcohol linalool is a common component in many essential oils and serves as a significant chemical signal for insects. One form, the (S)-(+)-linalool enantiomer, appeals to a broad range of pollinators, including bees and moths, which depend on the scent to locate flowers for nectar. Oils like lavender, which contain linalool, may attract these beneficial insects, or in high concentrations, certain pests. Other oils, such as cinnamon, lemon, and melissa, have specific compounds that lure in various pests like fungus gnats, leafminers, and Japanese beetles.
How Essential Oils Function as Repellents
Most people use essential oils for their ability to ward off unwanted insects, a function rooted in the oil’s interference with the insect’s sensory and nervous systems. These oils contain potent molecules that disrupt an insect’s ability to locate a host or a food source. The strong aroma of repellent oils effectively masks the carbon dioxide and skin odors that blood-feeding insects like mosquitoes use to track humans.
This olfactory disruption is the main defense mechanism of oils such as citronella, which contains citronellal and geraniol, compounds that overwhelm the insect’s chemoreceptors. Oil of Lemon Eucalyptus (OLE) is another effective repellent, containing para-menthane-diol (PMD), which confuses a mosquito’s sense of smell. Beyond masking, some essential oil components exhibit neurotoxic effects on insects.
Certain compounds, like those in cedarwood oil, interfere with the octopamine receptors in the insect’s nervous system, which are crucial for their survival. Other oils, including clove and cinnamon, contain insecticidal compounds capable of breaking down the protective outer layer of pests, leading to dehydration. Despite their potency, the effectiveness of essential oils as repellents is limited because the active compounds evaporate quickly, necessitating frequent reapplication.
Safe and Effective Use of Essential Oils
To use essential oils for insect management effectively and safely, proper application and dilution are required. Essential oils are highly concentrated and should never be applied directly to the skin without a carrier oil, such as coconut or jojoba oil, to prevent irritation. For topical repellent mixtures, a dilution of between 5% and 10% is generally used for adults.
A 5% dilution involves mixing approximately 30 drops of essential oil per one ounce (30 ml) of carrier oil. For continuous, passive protection in a small area, a diffuser can disperse the volatile compounds into the air. Because the repellent compounds evaporate rapidly, reapplication is necessary, often every one to two hours, to maintain a consistent barrier against insects.