PawPaw: A Source of Herbal Insecticide for Hair Shampoo

1. Volume 2, Issue 6, September 2009
Pawpaw: A Source of Herbal Insecticide for Hair
Shampoo
By: Charles Spielholz, Ph.D.
P
awpaw (genus Asimina) is a large shrub or small tree that grows in eastern
North America as far north as southern Canada, as far south as Georgia and as
far west as Texas and Nebraska. Pawpaw has large leaves and a large, heavily
seeded, edible fruit. The pulp of the fleshy fruit, which looks something like a papaya
that is curved like a banana, tastes like custard and is high in protein (Pawpaw is not
related to either of those tropical plants). The fruit is used to make jellies and jams and is
also used in baking cakes. Several species of pawpaw exist. The tree is not cultivated to
any significant extent. The genus is actually considered threatened or endangered in
several regions due to forest destruction.1
The pawpaw is interesting as a
botanical because the tree is not easily
susceptible to many insect pests.
Historically, Native Americans have used
the dry powder of pawpaw to eradicate
lice infestations. Chemical analysis of
different parts of the pawpaw show that
the pesticide activity, as measured using a standard brine shrimp assay, is highest in the
small twigs. The seeds, roots, bark and unripened fruit contain lower, but significant
pesticide activity, whereas the leaves and stem wood contain little or no pesticide
activity.2
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2. Volume 2, Issue 6, September 2009
The molecules responsible for the pesticide activity have been isolated and
identified as acetogenins. Acetogenins are part of a family of compounds known as
polyketides. Generally, polyketides are a naturally occurring class of molecules with
antibiotic, antifungal and insecticide properties. The structure of these molecules is very
complex making them difficult to synthesize; therefore acetogenins are isolated from
sources rich in the molecule. Pawpaw is rich in these molecules, but, as noted above, the
tree is not cultivated.3,4,5,6
Studies using extracts of pawpaw as an insecticide in hair shampoo were initiated.
Those initial studies indicated that hair shampoo containing a standardized extract of
pawpaw was 100% effective in removing both head lice and nits from scalp hair.
Preliminary research also showed that the active ingredients isolated from pawpaw did
not cause significant allergic contact dermatitis or skin irritation in a guinea pig
maximization test. These data indicate that pawpaw has the potential to be the active
botanical in an herbal shampoo to treat lice infestations. However, at the moment, no
such shampoo is commercially available although several websites describe recipes for
just such a shampoo.7,8
It must be noted at this point that there is also some data to indicate that pawpaw
extracts have cytotoxic effects on cancer cell lines grown in laboratory cultures.
However, there is no data currently available that clearly supports the efficacy or safety
of pawpaw to treat cancer (or any other disease). At the moment, pawpaw extracts have
been shown to be potentially useful externally and, in fact, may be dangerous when taken
interernally.9
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3. Volume 2, Issue 6, September 2009
So pawpaw has potential as an herbal remedy to treat lice infestations. It is quite
possible as lice and other insects develop resistance to lice shampoos currently on the
market, the natural insecticide properties of pawpaw may become very commercially
viable.
References
1) Little EL. National Audubon Society Field Guide to Tress, Eastern Region. New York, Alfred
A. Knopf, Inc. 1980.
2) Ratnayake S, Rupprecht JK, Potter WM, McLaughlin JL. Evaluation of various parts of the
paw paw tree, Asimina triloba (Annonaceae), as commercial sources of the pesticidal
annonaceous acetogenins. J Econ Entomol. 1992 Dec;85(6):2353-2356.
3) Ratnayake S, Fang XP, Anderson JE, McLaughlin JL, Evert DR. Bioactive constituents from
the twigs of Asimina parviflora. J Nat Prod. 1992 Oct;55(10):1462-1467.
4) Ratnayake S, Rupprecht JK, Potter WM, McLaughlin JL. Evaluation of the pawpaw tree,
Asimina tribola (Annonaceae), as a commercial source of the pesticidal annonaceous acetogenins.
In New Crops. Janick J, Simon JE (eds). New York, Wiley. 1993. pp 644-648.
5) Zhao GX, Rieser MJ, Hui YH, Miesbauer LR, Smith DL, McLaughlin JL. Biologically active
acetogenins from stem bark of Asimina triloba. Phytochemistry. 1993 Jul;33(5):1065-1073.
6) Johnson HA, Gordon J, McLaughlin JL. Monthly variations in biological activity of Asimina
tribola. In Progress in New Crops. Janick J (ed.). Arlington, ASHS Press. 1996. pp609-614.
7) Avalos J, Rupprecht JK, McLaughlin JL, Rodriguez E. Guinea pig maximization test of the
bark extract from pawpaw, Asimina triloba (Annonaceae). Contact Dermatitis. 1993 Jul;29(1):33-
35.
8) McCage CM, Ward SM, Paling CA, Fisher DA, Flynn PJ, McLaughlin JL. Development of a
paw paw herbal shampoo for the removal of head lice. Phytomedicine. 2002 Dec;9(8):743-748.
9) Lannuzel A, Michel PP, Caparros-Lefebvre D, Abaul J, Hocquemiller R, Ruberg M. Toxicity
of Annonaceae for dopaminergic neurons: potential role in atypical parkinsonism in Guadeloupe.
Mov Disord. 2002 Jan;17(1):84-90.
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