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JOURNAL OF MOSQUITO RESEARCH
90
by Japanese encephalitis (JE) virus belonging to
flaviviridae family. Around 3 billion natives of the
world population subsist in JE-endemic regions while
15,000 deaths out of more than 50,000 cases per
annum in Indian sub-continent alone (Kabilan et al.,
2004) are recorded. Domestic pigs and wild birds act
as natural reservoir hosts for this deadly virus.
Isolation of JE virus from diverse mosquito species
from tropics has made it possible to scientifically
conclude that culicine mosquitoes mainly
Culex
vishnui group (Culex vishnui, Cx. pseudovishnui
and
Cx. tritaeniorhynchus)
is the principal vector of JE
virus (Colless, 1957). The proverbial
Cx.
vishnui
group is pervasive and tenderly breeds in
paddy fields (Banerjee and Chandra, 2004) and other
water bodies with luxuriant vegetation. Their
profusion is directly related to the increase in rice
cultivation, shallow ditches and pools and that’s why
India, a major rice cultivating nation, is highly
endemic for JE. The situation is more likely to be
shoddier as pig rearing is growing exponentially along
with augmentation in both cropping sector and
cropping intensity (Keiser et al., 2005). Thus control
of
Cx. vishnui
group is need of the hour to minimize
the socio-economic crises.
Several synthetic insecticides have been developed
and employed in the field with considerable success to
control the vector but, they are proved to be
bio-magnifying toxic hazards due to their
non-selectivity,
residual
exposure,
and
non-biodegradability (Wattal et al., 1981). Along with
these, resistance to pesticides (Tabashnik, 1994) has
drawn attention to find out novel insecticides and
study of naturally occurring insecticides especially
from plant origin (Rawani et al., 2009; Chowdhury et
al., 2009) that are eco-friendly and target specific than
their synthetic equivalents.
Achyranthes aspera
, a common weed plant of
Amaranthaceae family, is distributed throughout
the tropical world. It is perennial around 25~118 cm
tall having quadrangular, juvenile with slightly puffed
up nodes and contradictory branching pattern
(Srivastav et al., 2011). The hairy surface of leaf bears
elliptic-oblong blade like structure and papery in
texture. The plant is known to exhibit significant
abortifacient activity in rabbits and mice and is found
to acquire contraceptive competence in rats pertaining
to its potent estrogenicity. Concerning our literature
review, no information is presented on its larvicidal
effect on
Cx. vishnui
group so far.
The purpose of present study was to evaluate the
larvicidal activity of the crude and solvent extracts of
A. aspera
leaves against
Cx. vishnui
group as target
species.
1 Results
The differential yields of all the solvent extracts
through Soxhlet extraction from 200 g of leaves were
as follows: petroleum ether extract, 6.73 g; n-hexane
extract, 2.78 g; ethyl acetate extract, 3.40 g;
chloroform: methanol (1:1, v/v) extract, 5.38 g;
acetone extract, 2.70 g; and absolute alcohol extract,
2.66 g. The consequences of the study pointed out that
the mortality rate of the larvae was highest at 0.5%
concentration of the crude extract when tested against
all the larval instars. The mortality percentages of the
all the instars with crude extract treatment were
presented in Table 1. Log probit analyses clearly
indicated augmentations in LC
50
(Figure 1) and LC
90
(Figure 2)
values (at 95% confidence level)
concerning larvicidal effects of later stages larvae
which were subsequently subordinated with increase
in exposure period (from 24 hours to 72 hours).
Figure 1 Graphical presentation of LC
50
values of crude extract
of
A. aspera
foliage against
Cx. vishnui
group
Journal of Mosquito Research