Friday, January 30, 2015

Spicebush, sulcatone, and mosquitoes

Aedes aegypti, wiki [8]
I fell down the google rabbit hole in a big way earlier today. I was digging around, looking for info on the chemical composition of some of my favorite scents from childhood. I wasn't doing this idly- essential oil companies sell these compounds. My though was this: wouldn't it be nice to blend a fragrance that captures where I grew up? 

Sweetgum Range, from wiki [6]
The aromas of a southern childhood that I settled on were forest soil, cedar, tomato leaves, gardenia, maple syrup, wet dog, and the fragrant terpenes from sweet gum (Liquidambar styraciflua) and spicebush (Lindera benzoin). Most of these were pretty easy to find. Oakmoss and vetiver conjure a forest floor, two varieties of cedarwood oil are manufactured in Texas alone, a tomato leaf accord is a popular perfume top note, blended jasmine and honey smells similar to gardenia, immortelle flower smells of maple syrup, costus of wet dog, etc etc. In fact, the resin of sweet gum’s Chinese cousin, also in the family Liquidambar, is a perfume staple. It is sometimes referred to as a variety of ‘styrax’.

Spicebush was the only fragrance without an obvious analog. Its crushed leaves smell of fresh citrus and camphoraceous cloves (like a hot toddy!). This lovely odor is referenced in its species epithet- ‘benzoin’. Derived from the the resin of trees in the genus Styrax, benzoin is another staple in perfumery. It smells of vanilla, warm powder, and musk. Spicebush was used by early American colonists as a substitute for allspice, and native peoples used it as a panacea, marinade, and fragrant tea. The spicebush swallowtail relies on spicebush as its only larval food source. It is also a preferred food of the gorgeous promethea silkmoths, and its bright red berries are a treat for the birds. 

Spicebush, image from wiki [7]
So what is it that makes spicebush smell so delicious? A 1994 journal article written on the chemistry of its distilled essential oils recorded notably high concentrations of 6-methyl-5-hepten-2-one (sulcatone), α-phellandrene, 1,8-cineole, and β-caxyophyllene [1]. This molecular information is how my descent into the deep internet began.

Sulcatone, a ketone which smells of fresh, fruity citrus and is found in lemongrass and tomatoes, is a controversial odorant in the world of tropical disease research. A recent study which garnered the notice of popular science publications identified sulcatone as a possible mosquito attractant. However, most other studies note it as a natural repellant. Seeing as sulcatone is present to some degree in existing natural insect repellants like lemongrass and citronella, and that it has the same characteristic citrus odor, I’m inclined to defer to the bulk of the literature.

Sulcatone, along with geranylacetone (fresh, rose-watery magnolia), are manufactured on the skin in greater amounts by some lucky individuals [5]. Sulcatone and geranylacetone mask your delicious blood smells from mosquitoes, which search out prey by sniffing the air for carbon dioxide and skin exudates. They do this by blocking key odorant receptor areas on a mosquito’s antennae [4].

Things that smell like this probably smell good to mosquitoes.
Octenol (1-octen-3-ol) is also manufactured on your skin. It smells of mushrooms (and is in fact a chemical mushrooms produce—think of this the next time you see a toad stool covered in flies), earth, and musk. This molecule is like catnip to insect parasites. Distressingly, octenol is sometimes used in perfumes to impart an earthy, animal base. This fact has rendered me skeptical of any perfume with base notes of vegetal decay. I’ll think twice before I apply a mossy fragrance in the summertime without a hefty dose of citrus and terpenes in accompaniment.

I almost wonder if humanity loves the smell of resins and terpenes because blood feeders detest them. It seems like an adaptive trait, to rub yourself with fragrant oils and disguise your scent from the small pests which would make a meal of you. Otherwise why would we cover up our natural odor, especially if it (supposedly) helps us identify potential mates? It is just a stray question, some food (or fragrance) for thought.

1. Tucker, A. O., Maciarello, M. J., Burbage, P. W., & Sturtz, G. (1994). Spicebush [Lindera benzoin (L.) Blume var. benzoin, Lauraceae]: a tea, spice, and medicine. Economic botany48(3), 333-336.

2. Logan, J. G., Birkett, M. A., Clark, S. J., Powers, S., Seal, N. J., Wadhams, L. J., ... & Pickett, J. A. (2008). Identification of human-derived volatile chemicals that interfere with attraction of Aedes aegypti mosquitoes. Journal of chemical ecology34(3), 308-322.

3.    Singh, N., Wang, C., Cooper, R., & Liu, C. (2012). Interactions among carbon dioxide, heat, and chemical lures in attracting the bed bug, Cimex lectularius L.(Hemiptera: Cimicidae). Psyche: A Journal of Entomology2012.

4.     Murphy, E. J., Booth, J. C., Davrazou, F., Port, A. M., & Jones, D. N. (2013). Interactions of Anopheles gambiae Odorant-binding Proteins with a Human-derived Repellent IMPLICATIONS FOR THE MODE OF ACTION OF N, N-DIETHYL-3-METHYLBENZAMIDE (DEET). Journal of Biological Chemistry,288(6), 4475-4485.

5.     Logan, J. G., Stanczyk, N. M., Hassanali, A., Kemei, J., Santana, A. E., Ribeiro, K. A., ... & Mordue, A. J. (2010). Arm-in-cage testing of natural human-derived mosquito repellents. Malaria journal9(1), 239.




1 comment:

  1. Maybe it's my mosquito-fighting DNA that makes me love garlic. :D