- The One Natural Mosquito Repellent That Really Works
- Lemon-scented gum, Spotted gum
- Growing Lemon Eucalyptus – How To Care For Lemon Eucalyptus
- Lemon Eucalyptus Information
- Lemon Eucalyptus Plant Care
- Lemon Eucalyptus Uses
The One Natural Mosquito Repellent That Really Works
First things first: If you’re looking for a science-backed method of repelling mosquitoes, you don’t need to shy away from synthetic repellents such as DEET and picaridin. DEET in particular has been widely used for decades, and studies show it protects against mosquitoes and ticks carrying malaria, West Nile virus, Zika virus, and Lyme, according to the Environmental Protection Agency. (Here’s a list of the best DEET and picaridin mosquito repellents that are recommended by experts.)
Prefer a natural option? Although there are a variety of products out there that claim to naturally repel the disease-carrying pests, most haven’t been proven to be effective. According to Stacy Rodriguez, a laboratory manager at New Mexico State University’s Molecular Vector Physiology Lab, you should also be skeptical of non-sprays, like the candles, bracelets, and even ultrasonic devices you’ve probably spotted on store shelves.
In a previous interview with Health, Rodriguez, who has extensively researched different types of repellents, said she would “strongly suggest” using a spray-on formula, such as those that contain DEET and picaridin, instead of wearable repellents.
If you do choose a natural alternative, though, there is one plant-based repellent that has been deemed effective in studies: oil of lemon eucalyptus extract.
RELATED: What’s the Best Mosquito Repellent? How to Buy the Right One for You
What is oil of lemon eucalyptus extract?
Oil of lemon eucalyptus extract (also known as p-menthane-3,8-diol, or PMD) is derived from the leaves of lemon eucalyptus trees and chemically synthesized, usually in the form of a spray.
The ingredient has earned its mosquito-repelling stripes in two NMSU studies led by Rodriguez. In the first, published in the Journal of Insect Science in 2015, researchers looked at eight commercially available repellents, two fragrances, and a vitamin B patch, and noted whether each formula repelled or attracted disease-carrying mosquitoes Aedes albopictus and Aedes aegypti when applied to participants’ hands. What they found: Cutter Lemon Eucalyptus Insect Repellent ($9; amazon.com), a plant-based spray that contains oil of lemon eucalyptus, was the only DEET-free formula to deliver strong and long-lasting results.
The second study, published in the Journal of Insect Science in 2017, looked at how effectively wearable repellents (such as the bracelets mentioned above) along with DEET and PMD sprays protect against female Ae. aegypti mosquitoes, the species most likely to spread Zika. Once more, the Cutter Lemon Eucalyptus Insect Repellent was found to be effective.
Animal studies on oil of lemon eucalyptus extract have not identified any adverse effects, although the FDA warns against using it on children under age 3, since it can irritate the eyes. Also important: The ingredient has not yet been studied for its ability to repel mosquitoes that carry diseases other than Zika, and unlike DEET, PMD repellents are not recommended for protection from ticks.
RELATED: 5 Reasons Mosquitoes Bite Some People and Not Others
Where to buy it
Mosquito repellents that contain oil of lemon eucalyptus extract are relatively affordable and can be purchased online, but make sure you read the labels carefully: Oil of lemon eucalyptus extract is not the same as lemon eucalyptus essential oil. Somewhat confusingly, the latter is often marketed as being a mosquito repellent as well, but offers a much shorter window of protection (one hour versus up to six for oil of lemon eucalyptus extract).
Look for a product that lists “oil of lemon eucalyptus” as the active ingredient, like Cutter Lemon Eucalyptus Insect Repellent, the brand that was observed in the two Journal of Insect Science studies, and Repel Lemon Eucalyptus Natural Insect Repellent ($7 for 4 oz.; amazon.com). Both can deliver up to six hours of protection, but make sure to reapply after that.
There is considerable confusion between ‘lemon eucalyptus essential oil’ and ‘oil of lemon eucalyptus’. Both are used as mosquito repellents but they have quite different chemical compositions and efficacy.
Lemon eucalyptus essential oil (sometimes simply called Lemon eucalyptus oil) is made by steam distilling the dried leaves and twigs of the lemon eucalyptus tree (Eucalyptus citriodora or Corymbia citriodora). A typical chemical profile for this essential oil is: citronellal (70-90%), citronellol (4-12%), and isopulegol (1-16%).
It also contains small quantities (trace -2%) of p-menthane 3,8-diol (PMD). PMD is a highly effective and long acting mosquito repellent but because it is only present in such small quantities in lemon eucalyptus essential oil the repellent properties of this essential oil are mainly due to its other components. Unfortunately these other components are relatively volatile and consequently the essential oil only has a short duration of action, typically less than an hour by arm-in-cage test. This is too short a time for it to be a reliable, convenient and effective repellent.
Lemon eucalyptus essential oil also has poor repellency against the aggressive aedes aegypti mosquito, a vector for many illnesses including zika fever, dengue fever, chikungunya and yellow fever. Due to its lack of efficacy lemon eucalyptus essential oil is not approved for use in countries with disease carrying mosquitoes.
It is however possible to process and purify lemon eucalyptus essential oil to reduce the citronellal content while increasing the PMD content. The process involves converting some of the citronellal into PMD, mirroring the natural conversion that occurs in the leaves of the lemon eucalyptus tree. This refined oil, with a minimum of 64% PMD, is commonly referred to as ‘oil of lemon eucalyptus’ (OLE).
In a nutshell, lemon eucalyptus essential oil is mainly citronellal with a small variable amount of PMD and is not approved for use in disease endemic areas due to its lack of efficacy. In contrast ‘oil of lemon eucalyptus’ is mainly PMD, which provides highly effective mosquito protection, and is approved for use in all disease endemic areas.
Unfortunately people often confuse these two quite distinct products. For example, journalists often report ‘oil of lemon eucalyptus’ studies as showing the efficacy of lemon eucalyptus essential oil. Even some aromatherapists, who should know better, perpetuate this confusion by recommending lemon eucalyptus essential oil as a mosquito repellent for protection against the zika virus. It is not approved for this purpose for good reason.
Here at Hebe Botanicals we refine our ‘oil of lemon eucalyptus’ until it is pure PMD. This ensures that SAFE has maximum effectiveness and that it is also entirely free of citronellal (hence very little smell). PMD is the only only plant-based active ingredient effective enough to be approved by the Centres for Disease Control (CDC) for use in disease endemic areas.
SAFE repellent has been independently tested (Study code 13/378) against the aedes aegypti mosquito and was found to be “highly effective”, providing over 6 hours complete protection from landings. In this comparative arm-in-cage test it outperformed Repel tropical strength repellent which contains two synthetic repellents (30% deet and 3.75% IR3535).
If you are thinking of purchasing lemon eucalyptus essential oil, or any other essential oil, for mosquito protection ask for an independent study demonstrating its effectiveness (the arm-in-cage complete protection time gold standard). Be prepared to be disappointed.
Dr Steve Humphries
Copyright © Hebe Botanicals
Even the CDC recommends this botanical ingredient as comparable to DEET for repelling disease-carrying insects.
Oh the dichotomies of DEET.
While DEET is the gold standard of insect repellents, it is also a strong synthetic chemical with a tarnished reputation. Known to the chemistry set as N,N-Diethyl-meta-toluamide, DEET was potentially linked to 14 cases of brain damage in the 1980s and 90s, inciting a flood of fear amongst consumers that has yet to recede.
Other reports of ill effects from the ingredients haven’t helped its cause. Scientific American describes one study, among others:
“A study conducted in the late 1980s on Everglades National Park employees to determine the effects of DEET found that a full one-quarter of the subjects studied experienced negative health effects that they blamed on exposure to the chemical. Effects included rashes, skin irritation, numb or burning lips, nausea, headaches, dizziness and difficulty concentrating.”
Meanwhile, in 2014 the EPA reported that after an interim review of DEET, they were unable to identify any risks of concern to “human health, non-target species or the environment.” So it’s a bit of a mixed bag.
A lot of times we are left weighing relative risks. What’s more important: Using the strongest weapons we can against disease-bearing insects, or staying away from synthetic chemicals that have been associated with health problems?
If you trust the EPA (this writer may question some of their findings, just sayin’) then repel to your heart’s content with DEET, following the instructions, of course.
BUT, there’s an alternative. Behold oil of lemon eucalyptus (OLE), the plant-based active ingredient derived from eucalyptus leaves and approved for efficacy by the CDC. The agency notes:
“CDC has evaluated information published in peer-reviewed scientific literature and data available from EPA to identify several types of EPA-registered products that provide repellent activity sufficient to help people reduce the bites of disease-carrying mosquitoes. Products containing the following active ingredients typically provide reasonably long-lasting protection.”
They list DEET, picaridin, IR3535, 2-undecanone, and oil of lemon eucalyptus. They describe it as such:
“Oil of lemon eucalyptus (OLE) or PMD (chemical name: para-menthane-3,8-diol), the synthesized version of OLE. Products containing OLE and PMD include, but are not limited to, Repel and Off! Botanicals. This recommendation refers to EPA-registered products containing the active ingredient OLE (or PMD). “Pure” oil of lemon eucalyptus (essential oil not formulated as a repellent) is not recommended; it has not undergone similar, validated testing for safety and efficacy and is not registered with EPA as an insect repellent.”
I know that some people shy away from botanicals when they’ve got manmade alternatives to take care of the job, but plants are powerful! There’s a reason why so many of our modern pharmaceuticals are synthesized plant ingredients.
Interestingly, a study published in Malaria Journal (if anyone knows about mosquito protection …) explains how plants have been used for millennia to repel insects. The use of plant-based oil formulations applied to the skin or clothes were first recorded in writings by ancient Greek, Roman and Indian scholars.
So how effective is it? Consumer Reports looked at plant-oil based repellents and found that one “product in our insect repellent ratings that contained 30 percent oil of lemon eucalyptus (OLE) did well in our tests, warding off mosquitoes and ticks for at least 7 hours.” They add that other products with plant oils – including cedar, cinnamon, citronella, clove, geranium, lemongrass, rosemary, and peppermint – “provided little protection, often failing in our tests within a half-hour.”
(Bonus: That one product that did so well in the Consumer Reports ratings? Repel Plant-Based Lemon Eucalyptus Insect Repellent. But be warned, as one Amazon reviewer put it, “omg does this stuff have a strong smell to it. it not only repels mosquitoes but I’m sure it could work on mother in laws, ex’s, lawyers, cops, etc. I mean my wife was sent away in tears so imagine what it must do to the bugs. it even says flammable on it?! this stuff is awesome!)
So there you have it. Even the decidedly-not-crunchy CDC finds this botanical alternative to DEET good enough to recommend as one of the five ingredients to use against disease-carrying pests. And Consumer Reports seconds the opinion in their meticulous testing. That’s good enough for me. The world already has enough synthetic chemicals being sprayed about, it’s time to let the plants do some heavy lifting.
Note: Just because OLE comes from trees, it’s still strong stuff. Be sure to read and follow product instructions closely.
Lemon-scented gum, Spotted gum
Tree to 50 m tall. Forming a lignotuber.
Bark smooth throughout, white to pink or coppery, often powdery, shedding in thin curling flakes, mottling of trunk often not pronounced.
Juvenile growth (coppice or field seedlings to 50 cm): stem rounded in cross-section, scabrid; juvenile leaves always petiolate, opposite for 2 or 3 pairs then alternate, ovate to lanceolate, 14–21 cm long, 4.5–8 cm wide, the base usually peltate for many nodes, green; petiole and lamina scabrid for many nodes.
Adult leaves alternate, petiole 1–2.5 cm long; blade narrowly lanceolate to falcate, (7)10–23 cm long, 0.6–2.8(3.5) cm wide, base tapering to petiole, concolorous, glossy, green, strongly penniveined, very densely reticulate, intramarginal vein parallel to and just within margin, oil glands island. Leaves lemon-scented when crushed or not so.
Inflorescences axillary compound, peduncles 0.3–1 cm long; buds 3 per umbel, pedicels 0.1–0.6 cm long. Mature buds obovoid to pyriform, 0.6–1 cm long, 0.5–0.7 cm wide, green to creamy, usually smooth, scar usually absent (outer operculum held to or almost to flowering, operculum scar therefore obvious only at late bud development if at all), operculum rounded to conical or slightly beaked, stamens inflexed, anthers cuboid or cuneate, versatile, dorsifixed, dehiscing by longitudinal slits (non-confluent), style long, stigma blunt or mop-like, locules 3, the placentae each with 5 vertical ovule rows (sometimes indistinct). Flowers white.
Fruit pedicellate (pedicels 0.1–0.7 cm long), urceolate or barrel-shaped, 0.8–1.5 cm long, 0.7–1.2 cm wide, disc descending, valves 3, enclosed.
Seed reddish black, glossy, 2.3–5 mm long, boat-shaped (flattened with a slight dorsal keel), dorsal surface smooth, not winged, hilum ventral.
Cultivated seedlings (measured at ca node 10): cotyledons reniform to orbicular; stems rounded in cross-section, setose/scabrid; leaves always petiolate with peltate insertion of petiole on lamina for at least 15 nodes, opposite for ca 3 pairs then alternating, ovate to lanceolate, 5–15 cm long, 2–8 cm wide, discolorous, dull, green. Leaves setose to scabrid on both sides and on petiole for more than 15 nodes.
A tall tree from temperate and tropical eastern Australia, found north from Coffs Harbour, New South Wales, throughout coastal and montane eastern and central Queensland inland to Chinchilla, the Carnarvon Range, Great Dividing Range east of Tambo, east from Townsville to Hughenden, and further north to Cooktown and Lakeland Downs on southern Cape York Peninsula. It prefers lighter loamy soils or skeletal soils and occurs as a component of dry sclerophyll forest and woodlands in hilly country. Corymbia citriodora has smooth, uniform to ± mottled bark whitish to coppery in season, and a conspicuously narrow-leaved crown which, in northern populations, is strongly lemon-scented. Pear-shaped buds are borne in clusters of 3 aggregated into compound inflorescences borne in the axils of leaves, whilst fruit are urn-shaped to barrel-shaped and to 0.7-1.2 cm wide and relatively thick-walled. Seeds are flattish and have a median dorsal keel (boat-shaped). Juvenile leaves are setose and have peltate leaf bases.
Corymbia citriodora is very similar to C. maculata, differing only in having slightly narrower crown leaves, less mottled bark and juvenile leaves that are still setose to scabrid (feel rough) on comparatively taller coppice growth. In C. maculata foliage is never lemon-scented, the juvenile leaves, whilst scabrid at first, soon become smooth on moderately low regrowth, whilst the bark is spotted due to the irregular pattern of shedding. Corymbia maculata is found from Taree south to Bega in New South Wales and disjunctly in the Mottle Range in eastern Victoria.
Corymbia citriodora and C. maculata both differ from a third species of spotted gum, C. henryi, found from the greater Brisbane area in Queensland south to Grafton in New South Wales. Corymbia henryi, described by Stan Blake in 1977, has generally larger and coarser juvenile and adult leaves and larger buds and fruit though the ranges in dimensions do overlap. In addition, with C. henryi fewer juvenile leaves have peltate leaf-bases than the other spotted gums.
In the classification of Brooker (2000) this species, as Eucalyptus citriodora, is placed in Eucalyptus subgenus Corymbia series Maculatae (the spotted gums). In their revision of the bloodwoods and ghost gums Hill & Johnson (1995) named this species Corymbia citriodora, in genus Corymbia section Politaria (the spotted gums).
Hill & Johnson (ibid. pages 389–90) segregated another species, Corymbia variegata, from C. citriodora, on the basis of leaves not being lemon-scented, combined with slight differences in juvenile and adult leaf dimensions and a more southerly distribution (from Coffs Harbour, New South Wales north to Maryborough, Carnarvon Range and Chinchilla in Queensland). McDonald & Bean (2000) reduced the status of C. variegata to C. citriodora subsp. variegata stating that the main difference was the absence of lemon-scent in foliage of subsp. variegata. Until quite recently subsp. variegata (as E. variegata F.Muell.) was regarded as belonging to E. maculata (see for example Chippendale (1988), Brooker & Kleinig (1994)). In EUCLID, C. variegata is included within a broader concept of C. citriodora. Further discussion of the taxonomic background can be found in the references cited. The degree of genetic and morphological difference between these spotted gum species and subspecies is slight indeed and is discussed in some detail in the following references: Lamour et al. (2000), Larsen (1965), McDonald et al. (2000).
Historically Mueller (1879, third decade) stated “E. citriodora can only be considered a variety of E. maculata, differing merely in the exquisite lemon-scent of its leaves….”. and he included both it and his 1859 species E. variegata in synonymy with the earlier described E. maculata.
In EUCLID we follow Hill & Johnson’s view restricting Corymbia maculata to New South Wales and eastern Victoria but treat C. variegata as a synonym of C. citriodora (in effect a citronellal-free chemotype of that species). All spotted gum species are important and well known in forestry, silviculture and in horticulture and there is considerable merit in recognizing specific distinction between the three core forms C. citriodora, C. maculata and C. henryi.
Botanists who want to go further and distinguish the two chemotypes of C. citriodora and C. maculata may find the following short key useful:
1. Foliage with strong lemon-scent, bark mostly not mottled: C. citriodora subsp. citriodora
1a. Foliage not lemon-scented, bark mottled
2. Seedling/juvenile leaves still with peltate leaf-bases at node 10: C. citriodora subsp. variegata
2a. Seedling/juvenile leaves mostly lacking peltate leaf-bases by node 9: C. maculata
MORE ABOUT CORYMBIA
MORE ABOUT SPOTTED GUMS
Flowering has been recorded in January, April, May, June, July, August, October and December.
Corymbia citriodora is an important forest tree, in demand for structural timber and for honey production. It also is popular in horticulture both within Australia and overseas.
Plants of C. citriodora are naturalized in the Darling Range near Mundaring, Western Australia, and also in suburban Sydney, New South Wales, having spread from plantings. In Kings Park, Perth, has a famous, beautiful avenue of this species planted many years ago, but it has spread to become a serious weed there also (Hussey et al., 1997).
Origin of Name
Corymbia citriodora: from the Latin citriodorus, lemon-scented.
Growing Lemon Eucalyptus – How To Care For Lemon Eucalyptus
Lemon eucalyptus (Eucalyptus citriodora syn. Corymbia citriodora) is an herb but it’s hardly a typical one. Lemon eucalyptus information suggests that the herb can grow to 60 feet high and even taller. For more lemon eucalyptus information, including how to care for lemon eucalyptus, read on.
Lemon Eucalyptus Information
This plant is an attractive Australian native. It has sword-shaped, gray-green leaves and tiny white flowers.
The lemon eucalyptus plant, also known as lemon-scented gum, has a more pungent smell than other citrusy herbs, like lemon verbena, lemon balm and lemon thyme. If you touch a leaf, the air is infused with the super-strong scent of lemon.
In fact, if you’ve every burned a citronella candle, don’t think it is scented with real lemon fragrance. Rather, it is made with oil from lemon eucalyptus bush leaves.
Lemon Eucalyptus Plant Care
If you are thinking of growing lemon eucalyptus, you need
to learn about lemon eucalyptus plant care. It isn’t a very difficult plant to grow.
You can grow the herb as an annual or a perennial. The plant in the wild is a broad-leafed evergreen bush or tree that can live a long time. Alternatively, you can grow it in a pot as an herb. Whichever way you want to grow the plant, you have to learn how to care for lemon eucalyptus plants.
You can start growing lemon eucalyptus outside if you live in U.S. Department of Agriculture plant hardiness zones 9 and higher. Be sure you have enough room, however. One way to limit the size of the plant is to grow it in a container. If you are growing lemon eucalyptus in a pot, the herb will not get taller than four feet.
These plants have shallow roots and resent root disturbance, so grow them in containers before you set them outside. However, in windy areas you need to plant them in their permanent locations while they are still fairly young to make sure they do not suffer from wind rock.
Think sun for the lemon eucalyptus. Don’t plant this herb in the shade or it will die. It will accept almost any type of soil, including nutritionally poor soil. Still, lemon eucalyptus plant care is easiest if you plant it in well-draining soil.
You’ll have to provide regular water for the first years. After the tree is established, it is drought tolerant.
Lemon Eucalyptus Uses
It’s not difficult to describe possible lemon eucalyptus uses. Generally, gardeners like growing lemon eucalyptus for its ornamental qualities and for the fragrance of its leaves.
In addition, however, it can be grown as a bee crop. The bush flowers are rich in nectar and excellent for attracting bees.