What essential oils, if any, are effective insecticides against drosophila melanogaster (the common fruit fly), and which, if any, may be feasible alternatives to traditional chemical-based insecticides.
Batches of flies roughly 15-20 large were placed in sealed tubes laid horizontally. A cotton ball saturated in a particular oil was placed in one end of each tube, and the flies response observed and recorded. Repeated for each oil.
Three controls were set up. One tested the flies’ response to a plain cotton ball, to make sure they were not startled by the sight or anything else. Another was soaked in vegetable oil, which is devoid of active compounds. This was to test if they were repelled by the physical properties of oil in general. Both of these controls came up clean. The flies didn’t care about the cotton ball or the vegetable oil. The third control was a direct application of vegetable oil. The physical nature of the oil suffocated the flies, meaning that all oils would kill the insects on direct contact.
Cinnamon oil derived from the leaves has shown to be very effective in killing mosquito larvae. I tested the oil derived from the bark. Untested as a potential insecticide. Primarily composed of cinnamaldehyde, at about 90%. Typically more expensive than leaf oil…but is it worth it?
The organic compound that gives cinnamon its smell and taste. Fungicidal and antimicrobial properties. Recognized for effectiveness against mosquito larvae. Unsaturated hydrocarbon with a carbonyl functional group (polarity, soluble in water) and an aromatic benzene ring (responsible for smell).
Quite effective at repelling, but not killing, insects. Flies showed strong aversion, but did not drop dead, even on contact. This means that it may be very good at protecting crops without killing the insects, and may delay genetic resistance.
Contains a-pinene, camphene, b-pinene, myrcene, limonene, cis-ocimene, camphor, linalool, methyl chavicol, y- terpineol, citronellol, geraniol, methyl cinnamate and eugenol. The big 3 are linalool at about 70%, limonene at 7%, and methyl cinnamate at 3%.
An organic compound classified as a terpene alcohol. It contains two double bonds and a hydroxyl group, the -OH. Highly Soluble in Water. Very common amongst aromatic herbs, such as mint. Known flea and cockroach insecticide.
A hydrocarbon classified as a cyclic terpene. Most commonly found in citrus. Contains an aromatic benzene ring, giving it its strong orange scent. Chiral molecule—more than one version. The one found in nature is D-Limonene Nonpolar, not soluble in water. Biodegradable, but because of its low flash point, is somewhat dangerous. As an insecticide, limonene destroys the wax that coats the inside of the insect's respiratory system.
The methyl ester of cinnamic acid. Moderately toxic by ingestion Benzene ring and carboxyl group. Highly polar, soluble in water. Unknown status as an insecticide.
Flies experienced severe muscle spasms. Strong effects on central nervous system. Did not die, even on contact with the cotton ball. Struggled to walk away. Potentially lethal as a sort of trap.
Contains pinene, cineol, camphor, camphene, bornyl acetate, borneol and verbenon, among others. Antiparasitical, antifungal, antibacterial Can trip seizures in those with epilepsy Camphor and pinene are the two big ones, though there are dozens of components shown to have insecticidal properties.
Complex hydrocarbon structure, nonpolar. Pinene is commonly used by insects to communicate. A pesticide made with pinene may confuse insects. Not commonly a direct insecticide.
Contains a carbonyl group, technically a lipid. Fungicide, insecticide, microbiocide Moderately toxic in large doses Recently banned by the FDA for sale in “raw” form. Banned products containing over 11% camphor. Mild skin irritant
Repelled flies greatly. Promising insecticide, and camphor levels are small enough to not pose a serious health risk with responsible usage. Wide range of constituents could be potentially effective against many insect species. A “silver bullet” insecticide.
D-limonene is the only real component The oil, in the sealed container, eventually did kill the flies, but the flies were not repelled and the rate of death was negligible. As an indirect pesticide, orange oil is not ideal, and its narrow range of constituents improves the odds of genetic resistance forming. Because of its availability, though, it is cheap and easy to apply, and direct application does destroy pests. Combining it with other oils is also a definite option. Proven effective at treating fire ant mounds.
Contains carvacrol, gamma-terpinene, p-cymene, and others. Wide range of constituents improves range of effectiveness. Expensive beyond all reason at the moment to produce and purchase.
Contains an alcohol group, making it polar with H-bonds and soluble in water. Aromatic benzene ring gives it its characteristic oregano scent. Tastes of pizza Halts microbial growth Known, but little used, pesticide No chemical danger, fit for human consumption
Contains cyclohexane, not to be confused with benzene. Some insecticidal properties Hydrocarbon, insoluble in water Occurs in relatively small quantities in oregano
Contains benzene ring Hydrocarbon, insoluble in water. The “P” comes from the position of the hydrocarbon side groups. At positions 1 and 4, it is Para, or P. Insecticide and insect growth regulator. Effective against mosquito larvae.
Extremely strong aversion. Those that got even remotely close spasmed wildly and fell to paralysis. Some died rapidly from the vapors. Potentially promising as a rapid treatment option for widespread infestation, though cost is an inhibitor.
Contains carvacrol and thymol, predominantly. Lower cost than oregano oil, though still not terribly affordable.
Controls mites and prevents mold growth in bee colonies. Selective nature of the chemical may serve to eliminate pests without disturbing beneficial insects. Thymol is dangerous to the environment and toxic to aquatic organisms and may cause long term adverse effects in the aquatic environment. Suspected of being a mutagen.
Caused moderate repulsion with moderate muscle spasms turning severe. Even on other side of tube, muscle spasms were evident. Several fly deaths. Lower cost and effectiveness show a bright future for this oil as an insecticide.
Commonly used as a mosquito repellant worldwide. Low cost, easy to produce. Contains geraniol, limonene, methyl isoeugenol, citronellol, and citronellal.
Monoterpenoid and alcohol. Soluble in both water and oil. Hydrophilic alcohol group and hydrophobic tail. Effective at repelling mosquitos. Also effective at attracting bees. Kills bad bugs, attracts good bugs. Win- win for farmer.
Commonly used in perfumes and insect repellants, but also as a mite attractant. Not all mites are bad, and many prey on other species of mites. So, again, this could be a win-win for farmers. Alcohol
Monoterpenoid. The main component that gives citronella its smell. Strong antifungal properties. Proven mosquito repellant.
General avoidance by the flies, though not a particularly strong aversion. Very gentle muscle spasms. Generally nonlethal. Low costs make it appealing, though it likely has a limited range of effectiveness. Best combined with other oils, or else left to repelling mosquitoes.
Of the tested oils, the three with the most market potential are rosemary, thyme, and basil, selected for their comparably low costs, wide range of constituents, and effectiveness as an insecticide. However, conventional insecticides remain more economical. Incentives will have to be presented for any major changes to take place. Genetically engineered crops may produce their own safe, natural insecticides.