Journal of Mosquito Research 2015, Vol.5, No.18, 1-8
3
mesh, 120 g) as admixture, subjected to column
chromatography (si gel, 100-200 mesh 400 g) to
obtain fractions by increasing polarity of eluents
viz
.,
hexane and ethyl acetate in the ratio of 100:0; 80:20;
60:40; 40:60; 20:80 and 0:100 respectively.
2.3 Larvicidal bioassay
Bioassay was carried out against laboratory reared
vector mosquitoes free of exposure to insecticides.
Standard WHO (2005) protocol with minor modifications
was adopted for the study. The tests were conducted in
glass beakers. Mosquito immatures particularly third
instar larvae were obtained from laboratory colonized
mosquitoes of F
1
generation. Larvicidal activity at test
concentrations of 25, 50, 75 and 100 ppm were
assessed. Twenty five healthy larvae were released
into each 250 ml glass beaker containing the required
test concentration and quantity of test solution. Larval
mortality was observed 24 hours post treatment.
Larvae were considered dead when they showed no
signs of movement when probed on their
respiratory siphon with a needle. A total of five trials
with three replicates per trial for each concentration
were carried out. Distilled water as control was run
simultaneously. The larval per cent mortality was
calculated and when control mortality ranged from
5-20% it was corrected using Abbott’s formula
(Abbott, 1925). SPSS 11.5 version package was used
for the determination of LC
50
and LC
90
values (SPSS,
2007). The percentage data obtained was angular
transformed. Data from mortality and effect of
concentrations were subjected to two way ANOVA
followed by Tukey’s test (P < 0.05) to determine the
difference in larval mortality between concentrations.
3 Results
Results revealed that six fractions (A, B, C, D, E and
F) were obtained. Amongst them, fraction ‘D’ showed
100.0, 99.2 and 97.6% mortality against third instar
larvae of
Aedes aegypti, Culex quinquefasciatus
and
Anopheles stephensi
at 100 ppm, respectively. Other
fractions showed minimum mortality (Table 1; Figure
1). No mortality was observed in control. The fraction
‘D’ exhibited LC
50
values of 27.20, 35.06 and 42.51
ppm against
Culex quinquefasciatus
,
Aedes aegypti
and
Anopheles stephensi
respectively (Table 2).
4 Discussion
One of the most effective alternative approaches under
the biological control programme is to explore the
Figure 1 Larvicidal activity of
Murraya koenigii
hexane leaf extract isolated fractions against vector
mosquitoes
floral biodiversity and enter the field of using safer
insecticides of botanical origin as a simple and
sustainable method of mosquito control (Ghosh et al.,
2012). The results of pesticidal and phytochemical
screenings of a number of higher plants based on
traditional knowledge strongly indicate that plants are
endowed with pesticidal properties that can be
harnessed cheaply for use in agriculture and related
fields. The need to use plant-based products arises
from the fact that the synthetic pesticides are harmful
to humans, and the entire ecosystem due to high
toxicity and persistence (Okwute, 2012). Several
studies have documented the efficacy of plant extracts
as the reservoir pool of bioactive toxic agents against
mosquito larvae. Mosquitoes in the larval stage are
striking targets for pesticides because they rear in
water and therefore very easy to handle in this
atmosphere (Nandita et al., 2008). Larviciding is more
effective since larvae are localized and restricted to a
small space before they emerge into adults (Howard et
al., 2007).
