Lemongrass (Cymbopogon species) is a tropical, perennial grass frequently used in Asian cuisine and appreciated for its bright, citrusy scent. It is also a common ingredient in aromatic products and is widely regarded as a natural way to deter insects. This has led to the popular belief that lemongrass can effectively keep flies away. To determine the truth behind this claim, it is necessary to examine the specific compounds and methods of application.
The Key Repellent Compounds in Lemongrass
The insect-repelling power of lemongrass comes from volatile organic compounds concentrated in its essential oil. The primary active component is citral, a mixture of two isomeric aldehydes (geranial and neral) that can make up over 70% of the oil, creating the strong lemon-like odor flies find highly aversive.
The mechanism of repulsion is a sensory disruption, not a toxic effect. High concentrations of citral overload the flies’ olfactory receptor cells on their antennae, masking the chemical signals they use to locate food and mates. This intense aroma triggers avoidance behavior.
Other compounds, such as citronellal and geraniol, also contribute to the repellent effect by interfering with insect neurotransmission. This disruption acts as a feeding deterrent, making treated surfaces unattractive to landing flies. Studies indicate significant repellency against house flies and stable flies when the essential oil is used in concentrated forms.
Effective Methods for Using Lemongrass Against Flies
The most effective way to utilize lemongrass is through its concentrated essential oil in a spray or diffuser. A repellent spray can be made by mixing 10 to 15 drops of essential oil with two ounces of water and an emulsifier like witch hazel or alcohol, which can be sprayed around entry points and on outdoor furniture. For indoor surface treatment, adding five milliliters of oil per liter of water to cleaning solutions is efficient for wiping down countertops. Localized protection can also be achieved by placing a few drops of oil on cotton balls near areas where flies gather.
Planting the actual lemongrass provides a much milder, less concentrated effect than the essential oil. The intact plant releases only low levels of volatile compounds, insufficient to deter large numbers of flies in an open area. To maximize the effect, the leaves must be crushed or bruised periodically to release the aromatic oils.
Limitations and Safety Considerations
A primary limitation of using lemongrass essential oil is its high volatility, causing the repellent effect to wear off quickly. The active compounds evaporate rapidly, meaning sprays and surface applications require frequent reapplication, often within a few hours, to maintain effectiveness.
Safety is a significant concern when handling the concentrated oil. Undiluted lemongrass essential oil is a known skin irritant that can cause redness, burning, and contact dermatitis. It must always be diluted with a carrier oil, such as coconut or jojoba oil, before topical application.
Lemongrass, in both plant and concentrated essential oil form, is toxic to household pets, including cats and dogs. Cats are particularly sensitive because they lack a specific liver enzyme necessary to metabolize the compounds. Ingestion or exposure to diffused oil poses a risk, so caution must be exercised to ensure pets cannot access the plant or the oil.