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JOURNAL OF MOSQUITO RESEARCH
10
In
C. rigidus
, monoterpenoids and sesquiterpenoids
have been identified as ingredients of the essential oil
in the leaves, seeds and fruits. Specifically,
triterpenoids (α-amyrin, betulinic acid and oleanolic
acid), tannins (pyragallol, catechol and β-sitosterol)
were found in arial parts (Jirovetz et al., 1997;
Praveen et al., 2012). Flavonoids (3’4’7-trihydroxy
flavonol, 3’4’7-trihydroxy flavone, 3’4’7-trihydroxy
flavonol-3-glycoside and 3’4’7-trihydroxy flavone-7-
galactoside) and monotriterpenes (γ-terpinene, α-terpeneol,
α-pinene, 1,8-cineol and limonene), melaleucin and
melaleucin acetate have also been reported to be
constituents of the leaves (Praveen et al., 2012).
The results of the present study are compared with
earlier reports. The bioactivity of ten plant oils, Cedar
wood (
Cedrus atlantica
(Endl.) Carrière), Citronella
(
Cymbopogon nardus
(Linn.) W. Watson), Clove
(
Myrtus caryophyllum
Spreng), Eucalyptus (
Eucalyptus
globulus
Labill. (Myrtaceae)), Lemon grass (
Cymbopogon
flexuosus
(Steud) Wats), Orange (
Citrus sinensis
(Linn.), Nutmeg (
Myristica fragrans
Houtt.),
Palmarosa (
Cymbopogon martini
Roxb.), Pine (
Pinus
radiate
D. Don) and Tulsi (
Ocimum sanctum
Tulsi)
were tested against the 3
rd
instar larvae of
Ae. aegypti
.
Larval mortality was observed after 24 h. Among the
plant oils tested, orange oil exhibited the highest
larvicidal activity with LC
50
of 85.93 ppm, followed
by Palmarosa with 88.78 ppm, Tulsi with 92.48 ppm
and Nutmeg oil with 93.62 ppm (Tennyson et al.,
2013). In addition, five essential oils from various
parts of five plant species i.e.
Acorus calamus
Linn.
(Acoraceae),
Mentha arvensis
Linn. (Lamiaceae),
Ocimum basilicum
Linn. (Lamiaceae),
Saussrea lappa
C.B. Clarke
(Asteraceae) and
Cymbopogon citrates
(DC.) Stapf (Apocynaceae) were investigated for their
larvicidal property against
Ae. aegypti
and
Cx.
quinquefaciatus
larvae. The highest larvicidal activity
was observed in the essential oil of
O. basilicum
against
Ae
.
aegypti
and
Cx. quinquefasciatus
with
LC
50
values of 75.35 ppm and 92.30 ppm, respectively
(Manzoor et al., 2013). Moreover, five major
components in essential oil from Pogostemon cablin
(Blanco) Benth. (Lamiaceae) (â-patchoulene, á-guaiene,
ã-patchoulene, á-bulnesene and patchouli alcohol)
were tested for pupicidal activity against three
medically important human vector mosquitoes at
100 mg/L. Among the five compounds tested,
patchouli alcohol was found to be the most effective
for pupicidal activity provided 28.44, 26.28 and
25.36% against
Ae. aegypti
,
An. stephensi
and
Cx.
quinquefasciatus
, respectively (Gokulakrishnan et
al., 2013).
Essential oils are presumed to interfere with basic
metabolic, biochemical, physiological and behavioural
functions of insects (Mann and Kaufman, 2012).
Though the mechanism of action (site effect) of the
two essential oils was not established in this study, yet
earlier, Ndione
et al
. (2013) reported the larvicidal and
cytopathologic effects of Suneem 1% (neem:
Azadirachta indica
A. Juss (Meliaceae)) on
An. gambiae
and
Cx. quinquefasciatus
larvae. In the control group,
within 24 to 48 h, in photonic microscopy level, an
epithelial cell layer was noted with a brush border
well developed, an adipose and muscle normal tissues.
The epithelial cells contain various organelles such as
mitochondria, dictyosoms, golgi apparatus, a network
endoplasmic reticulum and granular. In the treated
group, a gradual disappearance of cellular organelles
and significant vacuolation was observed. Cytoplasm
was less homogeneous. Ruiz et al. (2004) found a
significant vacuolation, swollen nuclei and elongated
epithelial cells of the mosquito larvae treated with
essential oil. These epithelial cells were disrupted at
the apical region with vesicle formation, lysis and
leakage of cytoplasm material into the gut lumen. In
addition, it is also known that the mosquito larvae and
pupae breathe through spiracles located on the 8
th
abdominal segment and therefore must come to the
surface frequently to breathe. The oils block the
spiracles, resulting in lack a respiratory siphon
(asphyxiation) and death (Kaufmann and Briegel,
2004; Rotimi et al., 2011).
In conclusion, the findings of the present study reveals
that essential oils from the
leaves of Cameroonian
P.
glandulosus
and
C. rigidus
can be effectively used as
potent mosquito larvicides and pupicides. Application
of these oils could be very useful to
reduce the larvae
and pupae of those vectors borne-diseases breeding in
wide variety of
containers, ranging from watering cans
and discarded
plastic bags to ground depressions and