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JOURNAL OF MOSQUITO RESEARCH
6
mosquito borne diseases rather than tackling the
diseases since it is known that “prevention is better
than cure” (Manzoor et al., 2013). To control those
vectors, chemical insecticides such as Temephos,
S-methoprene, Monomolecular films, Spinosad, Bti,
etc. have been used to reduce mosquito larvae or
pupae and as such prevent diseases (Brattsten and
Hamilton, 2012). Despite their effectiveness against
mosquitoes, chemical insecticides have some
disadvantages such as pollution, toxicity of residues to
the non-target organisms and resistance (Devine and
Furlong, 2007). To find new modes of action and to
develop active agents based on natural plant products,
efforts are made to develop phytochemical
insecticides (Gokulakrishnan et al., 2013). In 1991,
Sukumar et al. (1991) reviewed the use of natural
products derived from 344 different plant species to
control mosquito populations. Thus, the plant derived
products have received increased attention from
scientists and nowadays more than 2000 plant species
have already been screened as potent insecticides
providing possible lead candidates to replace synthetic
chemical insecticides for controlling mosquito in
aquatic stages (larvae and pupae) (Essam et al., 2005;
Anupam et al., 2012). In this regard, a survey of the
literature on insecticidal properties of essential oils
from the year 2004 onwards indicates that essential
oils from about 90 plant genera belonging to 38 plant
families were reported to have toxic properties against
mosquito larvae (Mann and Kaufman, 2012) and
pupae (Gokulakrishnan et al., 2013).
Plecthrantus glandulosus
Hook f (Lamiaceae) is a
plant which is adapted nearly to all types of areas and
altitudes (Abdel-Mogib et al., 2002). This plant is
found in West Africa flora (Ngassoum et al., 2001)
and also in Cameroon flora (Nukenine et al., 2013).
Still in Cameroon, it is plant whose leaves are
commonly used to protect stored grains and flour
(Nukenine et al., 2013; Goudoum et al., 2013).
C. rigidus
R. Br. (Myrtaceae) is known in folk
medicine for its anticough, antibronchitis effects and
its essential oils exhibited antifungal activity against
Phaeoramularia angolensis
(Jazet et al., 2009) and
Aspergillus flavus
(Dongmo et al., 2010).
In Cameroon, previous works showed the richness of
the two plant materials in volatile constituents
quantitatively and qualitatively (Nukenine et al., 2007;
Goudoum et al., 2012; Praveen et al., 2012).
Therefore, the aim of this work was to evaluate the
larvicidal and pupicidal potential of
P. glandulosus
and
C. rigidus
essential oils against
An. gambiae, Ae.
aegypti
and
Cx. quinquefasciatus
4
th
instar larvae and
early pupae.
1 Results
The yield of the essential oils extraction was 0.22%
(w/w) for
P. glandulosus
and 0.72% (w/w) for
C. rigidus
.
The larvicidal and pupicidal activities of
P.
glandulosus
and
C. rigidus
were found to be mosquito
species dependent and plant dependent.
The larvicidal toxicity of
P. glandulosus
essential oil
is against 4
th
instar larvae of
Ae. aegypti
,
An. gambiae
and
Cx. quinquefasciattus
after 24h of exposure
showed that
Ae. aegypti
was the most susceptible
species among the three target mosquito species in this
study with a LC
50
and LC
90
values of as small as 2.66
and 8.71 ppm, respectively (Table 1). Statistically,
there was no difference among all the concentrations
(F= 2.28; p>0.05).
An. gambiae
came in second
position to register a mortality rate of 76% with the
smallest concentration (12.5 ppm) and total
suppression from 50 ppm; displaying LC
50
and LC
90
values of 7.37 and 25.55 ppm, respectively. However,
Cx. quinquefasciattus
was the most resistant mosquito
species to record no mortality at the lowest
concentration and all tested larvae were killed at
concentrations of 100 and 150 ppm with LC
50
and
LC
90
values of 43.16 and 67 ppm, respectively.
The results of mosquito larvicidal activity of
C.
rigidus
essential oil against 4
th
instar larvae of
Ae.
aegypti
,
An. gambiae
and
Cx. quinquefasciatus
24 h
after treatment are summarised in (Table 2). From
these results,
Ae. aegypti
was also the most
susceptible mosquito species among those targeted in
this study achieving LC
50
and LC
90
values of 66.67
and 124.39 ppm, respectively and causing 32%
mortality at the lowest concentration of was 50 ppm.
As for
An. gambiae
which still came in second position