Plants with Pest Control Properties Against Urban Pests - Urban Insect Pests: Sustainable Management Strategies - page 218

Essential oils

herbivores from feeding, have direct toxic
effects, or be involved in recruiting
predators and parasitoids in response to
feeding damage. Some essential oils, such
as clove, rosemary, thyme, eucalyptus and
various mint species, have demonstrated
contact and fumigant toxicity towards a
wide spectrum of insects, including human
head lice (Tripathi et al ., 2009). Some of the
essential oils and their components are
chemosterilants, inducing sterility. Com-
pounds from essential oils such as
monoterpenes -pinene, cineole, eugenol,
limonene, terpinolene, citronellol, citro-
nellal, camphor and thymol have been
reported to be repellents against mosquitoes;
the sesquiterpene -caryophyllene is
repellent against Aedes aegypti ; phytol, a
linear diterpene alcohol, is repellent against
Anopheles gambiae ; and phenylethyl
alcohol, -citronellol, cinnamyl alcohol,
geraniol and -pinene, isolated from the
essential oil of Dianthus caryophyllum , are
repellents against ticks (Nerio et al ., 2010).
In some cases, the same terpenoid can repel
certain undesirable insects while attracting
more benefi cial insects; for example,
geraniol will repel house fl ies but attract
honey bees (Duke, 1990).
Recently the United States Environmental
Protection Agency (US EPA) has started
granting registration to certain plant oils
and oil derivatives and has placed botanical
oils with pesticidal properties under the
'exempt from EPA registration' category.
Many plant extracts that are listed and are
in current use include oils from cedar,
cinnamon, clove, cotton seed, garlic,
geranium, lemongrass, linseed, peppermint,
rosemary, soybean and thyme (US EPA,
2012). In addition, derivatives of botanical
oils such as cold-pressed neem oil received
registration in the USA as an insecticide for
use on outdoor and greenhouse agricultural
food and ornamental crops, and as an insect
repellent and insect growth regulator. Also
hydrogenated catmint oil is formulated into
products for direct application to human
skin to repel black fl ies, mosquitoes and
other biting insects (US EPA, 2012). Earlier,
countries such as Japan, Korea and also
the EU have considered reduced data

Essential oils from plants serve as a good
example of compounds that act as repellents
and discourage herbivory. The use of
essential oils extracted from aromatic plants
to control insect pests has been well
documented by Isman (2006) and Koul et al.
(2008). Essential oils demonstrate excellent
deterrent activity against a number of
insects, particularly haematophagous
insects (Nerio et al. 2010). In recent years,
the use of essential oils derived from
aromatic plants as low-risk insecticides has
increased considerably owing to their
popularity with organic growers and
environmentally conscious consumers
(Regnault-Roger et al. , 2012). Essential oils
are complex mixtures of volatile organic
compounds produced as secondary meta-
bolites in plants. Steam distillation of
aromatic plants yields essential oils, long
used as fragrances and fl avouring in the
perfume and food industries, respectively.
More recently they have become popular as
agents for aromatherapy. Essential oils are
characterized by a strong odour and
generally have a lower density than water.
Several plant families, for example,
Myrtaceae, Lauraceae, Rutaceae, Lamiaceae,
Asteraceae, Apiaceae, Cupressaceae,
Poaceae, Zingiberaceae and Piperaceae,
have been examined for essential oils with
anti-insect activities. Indeed, as many as
17,500 aromatic plant species have been
reported by Bruneton (1999). Approximately
3000 essential oils are known, out of which
300 have been commercially exploited for
the cosmetics, perfume and pharmaceuticals
industries (Bakkali et al ., 2008), apart from
their pesticidal potential (Chang and Cheng,
2002).
The compounds in essential oils exert
their action on insects through multiple
ways such as neurotoxic effects involving
several mechanisms, notably through
 - aminobutyric acid (GABA), octopamine
synapses and the inhibition of acetyl-
cholinesterase. With a few exceptions, their
mammalian toxicity is considered to be low
and environmental persistence is short.
These volatiles can deter insects or other