The effect of some plant extract on the developmental stages of mosquito species was conducted using Anopheles gambiae , Culex quinquefasciatus and Aedes aegypti at the first instar, second instar, third instar, fourth instar, pupae and adult. The plant used was scentleaf ( Ocimum gratissimum ). Soxhlet apparatus was used to extract each pulverized plant part using petroleum ether solvent. Plant extract from the petroleum ether solvent was used to test their effects on the developmental stages of each mosquito species. The result showed that the higher the developmental stages, the lower the percentage of mortality. It was also observed that as the time and concentration increases, the percentage of mortality also increases. Generally, the result showed that Anopheles gambiae is more susceptible in the extracts used followed by Aedes aegypti and then Culex quinquefasciatus .

1. Toxicity of Ocimum gratissimum leaf extract on the developmental stages
of different mosquito species.
Keywords:
Effective, extracts, developmental stages, mosquito, species, mortality.
ABSTRACT:
The effect of some plant extract on the developmental stages of mosquito
species was conducted using Anopheles gambiae, Culex quinquefasciatus and
Aedes aegypti at the first instar, second instar, third instar, fourth instar, pupae and
adult. The plant used was scentleaf (Ocimum gratissimum). Soxhlet apparatus was
used to extract each pulverized plant part using petroleum ether solvent. Plant
extract from the petroleum ether solvent was used to test their effects on the
developmental stages of each mosquito species. The result showed that the higher
the developmental stages, the lower the percentage of mortality. It was also
observed that as the time and concentration increases, the percentage of mortality
also increases. Generally, the result showed that Anopheles gambiae is more
susceptible in the extracts used followed by Aedes aegypti and then Culex
quinquefasciatus.
068-078 | JRAS | 2014 | Vol 2 | No 1
This article is governed by the Creative Commons Attribution License (http://creativecommons.org/
licenses/by/2.0), which gives permission for unrestricted use, non-commercial, distribution and
reproduction in all medium, provided the original work is properly cited.
www.janimalsciences.com
Journal of Research in Animal
Sciences
An International
Scientific Research Journal
Authors:
Ebe TE1
, Osuala FOU2
,
Njoku OO3
, Opara FN4
,
Iwuala MOE5
Institution:
1. Department of
Environmental Technology,
School of Environmental
Technology, Federal
University of Technology,
Owerri, Imo state, Nigeria.
2, 3, 4 and 5. Department of
Biological Science, School
of Science, Federal
University of Technology,
Owerri, Imo state, Nigeria.
Corresponding author:
Ebe TE.
Email:
Web Address:
http://janimalsciences.com/
documents/AS0023.pdf. Dates:
Received: 23 Sep 2013 Accepted: 22 Oct 2013 Published: 28 Feb 2014
Article Citation:
Ebe TE, Osuala FOU, Njoku OO, Opara FN and Iwuala MOE.
Toxicity of Ocimum gratissimum leaf extract on the developmental stages of different
mosquito species.
Journal of Research in Animal Sciences (2014) 2(1): 068-078.
Journal of Research in Animal Sciences An International Scientific Research Journal
Original Research
JournalofResearchinAnimalSciences

2. INTRODUCTION
Since the early part of the last century,
researchers have ascertain the importance of mosquito
vectors of human pathogens. Mosquitoes have been a
constant impediment to progress, causing great suffering
on account of their blood-sucking habits and their ability
to transmit disease pathogens.
Yearly, large amounts of money is mapped out
for mosquito control which involves the use of synthetic
(artificial) pesticides; in most cases they
areorgano- chlorines, cabamates, organophosphates etc.
These chemicals have adverse effect on the environment
and man, and some are very persistent and take a long
time to breakdown and are easily moved by wind or
water to any part of the earth. Persistent pesticides have
also been discovered in animals including humans.
Another problem that is associated with persistent
chemicals used as pesticides is its bioaccumulative effect
in humans. Furthermore, some pests are resistant to
synthetic pesticides therefore, they have little or no effect
on the control of these pests which tend to impose
problem on the environment. However, extracts of some
plants with insecticidal properties have been tried in the
recent past for the control of variety of insect pests and
vectors. For instance, Ocimum gratissimum commonly
called “scent leaf” or “fever plant” is a small, smooth
shrub with many branches and are commonly found in
the tropics and widely distributed because of its
medicinal uses. Ocimum gratissimum (Scent leaves)
belongs to the family Lamiaceae and it is an aromatic
perennial herb widely grown in Nigeria. It is commonly
known as scent leaf or locally, it is called Nchuanwu by
the Igbos, Effirim by the Yorubas and Dai doyatagida by
the Hausa (Orwa et al., 2009; Okoli et al., 2010). The
plant can be used for the treatment of diseases like
malaria (Rabelo et al., 2003). Edeoga et al., 2006,
reported the presence of alkaloids and flavonoids in the
plant. There is presence of bioactive compounds like
eugenol, thymol, camphor and linolool on its leaf
essential oil (Rabelo et al., 2003; Lemos et al., 2005).
METHODOLOGY
Collection of mosquito species
The eggs of the different species of Mosquito
(Aedes aegypti, Anopheles gambiae and
Culex quinquefasciatus) were collected from the egg
colony at the National Arbovirus and Vector Research
Centre, Enugu, Enugu State, Nigeria, and were reared in
the laboratory.
Collection of plant parts
Fresh plant parts were collected at Amudi in
Ezinihitte Mbaise Local Government Area of Imo State
and identified by a botanist in Forestry and Wild Life
Department of Federal University of Technology,
Owerri. Dead leaves were removed together with insect
larvae from the twigs. The plant part was carefully
washed, rinsed with tap water and air dried at room
temperature of 28±1o
C for five days and stored in air
tight glass containers for further use (Okigbo et al.,
2010).
Preparation of plant extract
The completely dried plant part was ground with
Binatone Mx10 blender and sieved to obtain a fine
powder of the plant part.150 grams of each pulverised
plant part was placed in a plain sheet of white paper, then
placed in the timbel of the soxhlet apparatus
compartment using petroleum ether extraction solvent
(Okigbo et al., 2010).
Preparation of test material
Larval and pupal stages.
Stock solution was prepared by dissolving 5g of
the extract in 150mls of water into which three drops of
acetone was added to emulsify the oil in water and then
making it up to 250ml by mixing with distilled water in
standard flask. All the test solutions were made by
pipetting 5ml-50ml of the stock solution and introduced
into 240ml, 235ml to 195ml of distilled water
respectively in separate labelled500ml bowls making it
Ebe et al.,2014
069 Journal of Research in Animal Sciences (2014) 2(1): 068-078

3. up to 245ml in volume (WHO, 1981 )
Adult stage
Stock solution was prepared by dissolving also
5g of the extract in 150mls of water and three drops of
acetone is added to emulsify the oil in water and then
making it up 250ml by mixing with distilled water in
standard flask. All the test solutions were made by
pipetting 5-50ml of the stock solution and impregnate a
white paper with the different concentrations of the test
plant extract. The impregnated papers were placed
separately in a plastic container of 500ml size and
covered with a mosquito net of 0.1cm mesh with a small
opening and then tied with a rubber band.
Susceptibility test
LARVA/PUPA
Twenty specimens of each stage of the different
mosquito were picked using rubber pipette and placed in
small separate specimen bottles containing 5ml of water
and then exposed to each of the concentrations of the
extract giving a final volume of 250ml in the bowls.
Quaker oat powder was used to feed the larvae
every twenty-four hours (Mbgemena, 2010). Three
replicates for each of the test concentration and control
(without plant extracts) were tested for anti-larval/pupal
effects. The larval/pupae mortalities were recorded at
intervals of 8 hours for 48 hours exposure. All the
mortalities were counted and recorded.
Adult stage
Twenty specimens from each of the mosquitoes
types were collected from the rearing cage using
aspirator and introduced into the plastic containers
containing impregnated paper of varying concentrations
(WHO, 1999, WHO, 1992 and Siriporn and Mayura,
2011); control experiment was set-up by exposing
mosquito species to an untreated paper . Each test was
performed in three replicates with simultaneous control
sets (Siriporn and Mayura, 2011).
RESULTS
From the Table 1, after 8hrs of exposture,
Anopheles gambiae recorded 100% mortality at 50mg/ml
at the first instar stage which decreases with increase in
developmental stages while both Culex quinquefasciatus
and Aedes aegypti recorded 97.5% at the same
concentration and stage which also decreases with
increase in developmental stages.
Table 2 shows that Anopheles gambiae recorded
100% mortality from 35mg/ml-50mg/ml at the first instar
stage and 50mg/ml at the second instar stage while less
than 100% mortality was recorded from the third instar-
the adult stages.
Furthermore, Aedes aegypti recorded 100%
mortality from 40mg/ml-50mg/ml at the first instar
and at 50mg/ml at the second stage and less than
100% from third instar- adult stages. Likewise, in
Culex quinquefasciatus recorded 100% mortality from
45-50mg/ml only at the first instar while from second
instar-adult stages recorded less than 100%.
In Table 3, after 24hrs exposture,
Anopheles gambiae recorded 100% mortality from first
instar to fourth instar at 25-50mg/ml, 35-50mg/ml, 45-
50mg/ml and 50mg/ml respectively.
Also Culex quinquefasciatus recorded 100%
mortality in first and second instar stages at 30-50mg/ml
and 45-50mg/ml respectively while Aedes aegypti also
recorded also 100% mortality in the first and
second instar stages at 25-50mg/ml and 35-50mg/ml
respectively.
After 32hrs of exposture, 100% mortality was
recorded in Anopheles gambiae from the first instar
pupa stages from 5 to 50mg|ml respectively.
Culex quinquefasciatus recorded 100% mortality from
the first instar to third instar stages from 20-50mg/ml,
30-50mg/ml and 50mg/ml respectively. While
Aedes aegypti recorded 100% mortality from first instar to
fourth instar stagefrom15-50mg/ml,25-50mg/ml, 45-50mg/
ml and 50mg/ml respectively. This is shown in table 4.
Ebe et al., 2014
Journal of Research in Animal Sciences (2014) 2(1): 068-078 070

4. Ebe et al.,2014
071 Journal of Research in Animal Sciences (2014) 2(1): 068-078
Table 1:Effect of Ocimum gratissimum leaf on different stages of three mosquito species after eight hours.
Mosquito species Conc. of plant
Stages of mosquito species
Extract (Mg/Ml)
1 2 3 4 5 6
Anopheles gambiae 5 45.00 25.00 15.00 2.33 0.00 0.00
10 50.00 30.00 20.00 7.67 0.00 0.00
15 55.00 40.00 25.00 17.67 7.67 0.00
20 65.00 45.00 32.33 27.67 17.67 8.00
25 72.33 55.00 37.33 37.33 27.33 13.00
30 80.00 60.00 45.00 40.00 30.00 23.00
35 90.00 67.67 57.67 52.33 42.33 18.00
40 95.00 77.33 67.67 57.33 47.67 33.67
45 97.33 85.00 77.33 65.00 55.00 38.00
50 100.00 92.67 85.00 72.67 62.67 39.67
Culex quinquefasciatus 5 25.00 7.67 00.00 00.00 00.00 00.00
10 35.00 15.00 00.00 00.00 00.00 00.00
15 42.67 20.00 2.67 00.00 00.00 00.00
20 55.00 25.00 7.67 2.67 00.00 00.00
25 60.00 35.00 12.67 5.00 2.33 00.00
30 65.00 45.00 20.00 10.00 7.33 00.00
35 72.67 55.00 25.00 20.00 12.33 3.00
40 82.67 60.00 30.00 27.33 20.00 8.00
45 92.67 70.00 40.00 32.33 25.00 14.67
50 97.33 75.00 45.00 40.00 30.00 19.67
Aedes aegypti 5 32.33 20.00 2.33 00.00 00.00 00.00
10 40.00 25.00 5.00 00.00 00.00 00.00
15 50.00 30.00 7.67 2.67 00.00 00.00
20 60.00 40.00 12.33 7.67 2.33 00.00
25 65.00 45.00 17.67 12.67 7.67 00.00
30 70.00 50.00 27.33 20.00 17.67 1.33
35 77.33 65.00 35.00 27.33 22.67 9.67
40 85.00 70.00 45.00 37.67 27.67 13.00
45 90.00 75.00 47.67 42.67 32.67 19.67
50 97.67 85.00 60.00 52.67 42.33 24.33

5. Ebe et al.,2014
Journal of Research in Animal Sciences (2014) 2(1): 068-078 072
Mosquito species Conc. of plant extract Different stages of mosquito species
1 2 3 4 5 6
Anopheles gambiae 5 65.00 45.00 37.67 20.00 10.00 00.00
10 70.00 50.00 45.00 27.67 17.33 00.00
15 75.00 60.00 55.00 32.67 22.67 1.00
20 80.00 65.00 60.00 47.67 37.67 11.00
25 87.67 75.00 67.33 55.00 45.00 16.00
30 95.00 80.00 72.67 62.67 52.67 26.00
35 100.00 85.00 77.33 70.00 60.00 31.00
40 100.00 90.00 82.67 77.33 67.67 37.67
45 100.00 97.67 92.67 82.33 72.67 41.00
50 100.00 100.00 97.33 92.67 82.67 42.67
Culex quinquefasciatus 5 45.00 30.00 2.33 2.67 00.00 00.00
10 55.00 35.00 7.67 7.33 2.33 00.00
15 60.00 47.67 12.67 15.00 7.67 00.00
20 70.00 52.33 25.00 20.00 12.67 00.00
25 80.00 57.33 30.00 25.00 17.33 00.00
30 85.00 70.00 35.00 30.00 22.67 2.67
35 92.67 75.00 45.00 37.33 32.67 6.00
40 97.33 80.00 50.00 42.67 37.67 11.00
45 100.00 90.00 60.00 47.67 42.33 17.67
50 100.00 95.00 65.00 60.00 47.33 22.67
Aedes aegypti 5 50.00 40.00 20.00 2.33 2.33 00.00
10 60.00 45.00 25.00 7.33 7.67 00.00
15 67.67 50.00 30.00 20.00 20.00 00.00
20 75.00 60.00 37.67 25.00 25.00 00.00
25 85.00 65.00 45.00 30.00 30.00 00.00
30 90.00 70.00 50.00 35.00 35.00 4.33
35 95.00 85.00 57.67 45.00 45.00 12.67
40 100.00 92.67 62.33 55.00 55.00 16.00
45 100.00 95.00 70.00 60.00 60.00 22.67
50 100.00 100.00 77.67 67.67 57.67 29.33
Table 2: Effect of Ocimum gratissimum leaf on different stages of mosquito species after sixteen hours

6. Ebe et al.,2014
Mosquito species Conc. of plant extract (mg/ml) Different stages of mosquito species
1 2 3 4 5 6
Anopheles gambiae 5 85.00 65.00 62.33 47.67 35.00 0.00
10 90.00 70.00 70.00 52.67 40.00 1.67
15 95.00 80.00 75.00 57.67 45.00 5.00
20 97.33 85.00 80.00 62.67 50.00 15.00
25 100.00 95.00 85.00 75.00 62.33 20.00
30 100.00 97.33 90.00 80.00 72.67 30.00
35 100.00 100.00 92.67 85.00 75.00 35.00
40 100.00 100.00 95.00 90.00 80.00 41.67
45 100.00 100.00 100.00 97.33 87.33 45.00
50 100.00 100.00 100.00 100.00 92.67 46.67
Culex
Quinquefasciatus
5 65.00 50.00 20.00 12.33 12.67 00.00
10 75.00 55.00 25.00 20.00 17.33 00.00
15 80.00 67.67 32.67 32.67 30.00 00.00
20 85.00 75.00 40.00 40.00 37.33 00.00
25 97.67 80.00 50.00 45.00 42.33 3.33
30 100.00 90.00 55.00 50.00 47.33 6.67
35 100.00 95.00 65.00 55.00 52.67 10.00
40 100.00 97.33 70.00 60.00 57.67 15.00
45 100.00 100.00 80.00 67.33 62.33 21.67
50 100.00 100.00 85.00 77.67 62.33 26.67
Aedes aegypti 5 70.00 57.33 40.00 12.67 12.33 00.00
10 80.00 62.67 50.00 25.00 22.67 00.00
15 85.00 67.33 55.00 37.33 37.67 00.00
20 95.00 72.33 60.00 45.00 42.33 00.00
25 100.00 77.67 65.00 50.00 47.33 3.33
30 100.00 92.33 70.00 55.00 52.67 8.33
35 100.00 100.00 75.00 60.00 57.67 16.67
40 100.00 100.00 80.00 70.00 67.33 20.00
45 100.00 100.00 85.00 75.00 72.33 26.67
50 100.00 100.00 95.00 85.00 75.00 33.33
Table 3: Effect of Ocimum gratissimum leaf on different stages of mosquito species after twenty four hours.
073 Journal of Research in Animal Sciences (2014) 2(1): 068-078

7. Ebe et al.,2014
Journal of Research in Animal Sciences (2014) 2(1): 068-078 074
Mosquito species Conc. of plant extract (mg/ml) Different stages of mosquito species
1 2 3 4 5 6
Anopheles gambiae 5 100.00 85.00 72.33 60.00 50.00 1.67
10 100.00 90.00 80.00 65.00 55.00 8.33
15 100.00 97.33 87.67 77.67 65.00 15.00
20 100.00 97.67 92.33 82.33 70.00 25.00
25 100.00 100.00 97.33 85.00 77.33 31.67
30 100.00 100.00 97.67 92.67 82.33 38.33
35 100.00 100.00 100.00 97.67 87.67 45.00
40 100.00 100.00 100.00 100.00 92.33 50.00
45 100.00 100.00 100.00 100.00 97.33 51.67
50 100.00 100.00 100.00 100.00 100.00 58.33
Culex
quinquefasciatus
5 80.00 67.67 37.33 22.67 22.33 00.00
10 87.33 72.33 45.00 32.33 32.67 00.00
15 97.33 82.67 50.00 45.00 40.00 3.33
20 100.00 92.33 57.67 52.67 50.00 6.67
25 100.00 97.33 67.67 62.67 57.67 13.33
30 100.00 100.00 75.00 70.00 62.67 20.00
35 100.00 100.00 85.00 75.00 67.33 25.00
40 100.00 100.00 90.00 80.00 67.67 28.33
45 100.00 100.00 95.00 85.00 72.33 36.67
50 100.00 100.00 100.00 92.67 77.33 41.67
Aedes aegypti 5 90.00 75.00 57.67 30.00 27.33 00.00
10 97.67 80.00 62.33 40.00 37.33 1.67
15 100.00 90.00 67.67 55.00 52.67 3.33
20 100.00 95.00 72.67 60.00 57.67 6.67
25 100.00 100.00 77.33 65.00 62.33 13.33
30 100.00 100.00 82.33 75.00 72.33 20.00
35 100.00 100.00 92.33 80.00 77.33 28.33
40 100.00 100.00 97.33 87.67 82.33 31.67
45 100.00 100.00 100.00 95.00 87.67 38.33
50 100.00 100.00 100.00 100.00 92.33 45.00
Table 4: Effect of Ocimum gratissimum leaf on different stages of mosquito species after thirty two hours

8. Ebe et al.,2014
Mosquito species Conc. of plant extract (mg/ml) Different stages of mosquito species
1 2 3 4 5 6
Anopheles gambiae
5 100.00 97.67 82.67 70.00 57.33 8.33
10 100.00 100.00 90.00 77.33 67.67 15.00
15 100.00 100.00 95.00 82.67 72.67 20.00
20 100.00 100.00 97.67 90.00 82.67 28.33
25 100.00 100.00 100.00 95.00 87.33 36.67
30 100.00 100.00 100.00 97.67 92.33 40.00
35 100.00 100.00 100.00 100.00 97.33 51.67
40 100.00 100.00 100.00 100.00 100.00 56.67
45 100.00 100.00 100.00 100.00 100.00 65.00
50 100.00 100.00 100.00 100.00 100.00 75.00
Culex
quinquefasciatus
5 97.33 85.00 47.33 37.67 37.67 00.00
10 100.00 90.00 57.33 45.00 42.33 1.67
15 100.00 97.33 65.00 62.33 47.33 8.33
20 100.00 100.00 75.00 70.00 57.33 16.67
25 100.00 100.00 85.00 75.00 67.67 23.33
30 100.00 100.00 95.00 87.67 72.67 30.00
35 100.00 100.00 100.00 92.67 77.67 36.67
40 100.00 100.00 100.00 97.67 82.67 41.67
45 100.00 100.00 100.00 100.00 87.67 50.00
50 100.00 100.00 100.00 100.00 92.33 56.67
Aedes aegypti
5 100.00 90.00 70.00 45.00 42.33 1.67
10 100.00 95.00 75.00 60.00 52.33 3.33
15 100.00 100.00 80.00 72.33 62.33 6.67
20 100.00 100.00 85.00 80.00 77.67 15.00
25 100.00 100.00 95.00 85.00 80.00 21.67
30 100.00 100.00 97.67 92.33 87.67 28.33
35 100.00 100.00 100.00 97.33 90.00 36.67
40 100.00 100.00 100.00 100.00 92.67 45.00
45 100.00 100.00 100.00 100.00 97.67 56.67
50 100.00 100.00 100.00 100.00 100.00 65.00
Table 5: Effect of Ocimum gratissimum leaf on different stages of mosquito species after forty hours
075 Journal of Research in Animal Sciences (2014) 2(1): 068-078

9. Ebe et al.,2014
Journal of Research in Animal Sciences (2014) 2(1): 068-078 076
Mosquito species Conc. of plant extract (mg/ml) Different stages of mosquito species
1 2 3 4 5 6
Anopheles gambiae 5 100 100.00 95.00 80.00 70 21.67
10 100 100.00 100.00 90.00 77.67 28.33
15 100 100.00 100.00 97.33 87.33 36.67
20 100 100.00 100.00 100.00 92.67 43.33
25 100 100.00 100.00 100.00 97.67 50.00
30 100 100.00 100.00 100.00 100.00 65.00
35 100 100.00 100.00 100.00 100.00 70.00
40 100 100.00 100.00 100.00 100.00 75.00
45 100 100.00 100.00 100.00 100.00 80.00
50 100 100.00 100.00 100.00 100.00 90.00
Culex
quinquefasciatus
5 100 97.36 65.00 47.33 47.33 3.33
10 100 100.00 75.00 57.33 55.00 8.33
15 100 100.00 85.00 72.33 60.00 16.67
20 100 100.00 95.00 87.67 65.00 21.67
25 100 100.00 100.00 95.00 77.33 31.67
30 100 100.00 100.00 97.67 85.00 38.33
35 100 100.00 100.00 100.00 90.00 45.00
40 100 100.00 100.00 100.00 92.67 53.33
45 100 100.00 100.00 100.00 97.33 60.00
50 100 100.00 100.00 100.00 100.00 68.33
Aedes aegypti 5 100 100.00 82.67 65.00 62.33 3.33
10 100 100.00 87.67 75.00 67.33 11.67
15 100 100.00 95.00 87.67 77.67 15.00
20 100 100.00 97.67 95.00 87.33 23.33
25 100 100.00 100.00 97.33 90.00 31.67
30 100 100.00 100.00 100.00 95.00 35.00
35 100 100.00 100.00 100.00 95.00 48.33
40 100 100.00 100.00 100.00 100.00 56.67
45 100 100.00 100.00 100.00 100.00 68.33
50 100 100.00 100.00 100.00 100.00 76.67
Table 6: Effect of Ocimum gratissimum leaf on different stages of mosquito species after forty eight hours.

10. Moreover, after 40 hours of exposure,
Anopheles gambiae and Aedes aegypti showed 100%
mortality from the first instar to pupae stages. The first
instar recorded 100% mortality in both species from
5-50mg/ml while the concentration in the other stages
varied. Culex quinquefasciatus recorded 100% mortality
from the first instar to fourth instar stages at varying
concentration as shown in table 5. The same is applicable
to the result obtained after 48hrs of exposure except that
100% mortality was recorded from 5-50mg/ml in both
the first and second instar stages of both
Anopheles gambiae and Aedes aegypti and from 5-50mg/
ml at the first instar stage of Culex quinquefasciatus.
DISSCUSION
The present study confirmed that the plant part
extract used was a potential agent for the control of
mosquito population. The intensive use of synthetic
organic chemical larvicide or adulticide produce side
effects on many beneficial insects and also poses both
acute and chronic threat to the environment and also
resistance in major vector species. Toxicity of the tested
plant extracts against the four instars of larvae, pupae
and adult of Anopheles gambiae, Culex quinquefaciatus
and Aedes aegypti varied according to the concentration
of the extract, the developmental stage, the species of
mosquito exposed and the duration of exposure. The
percentage mortality decreases by the stage of growth
with more deaths in Anopheles gambiae followed by
Aedes aegypti and then Culex quinquefaciatus. This is
because Anopheles gambiae breed and thrive well in
fresh water unlike the Culex quinquefasciatus that thrives
in polluted water and thereby having more resistance to
the extracts used (Subra, 1980). The mortality rate
decreases with increase in growth; this means that the
highest mortality occurred at the first instars of the
mosquito species with different extract while the least
occurred at the adult stage. Similar results were also
obtained by Murugan and Jeyabalan (1999) and
Prophiro et al., (2008). This may be due to its feeding
habit. The larvae feed voraciously in water (Donald
2008); so during the course of their feeding they take
more of the extract and also the toxic environment affect
with them, while the pupae and adult do not take enough
of the extract because they are not feeding on the extract
but are affected by the toxic environment only. Senthil
Kumar et al., (2009) reported that lethality varied by type
of mosquito and extract: C. citratus, Justicia gendarussa
and Centella asiatica were found to be most effective
against Anopheles stephensi, C. citratus showed toxicity
against Culex quniquefasciatus larvae giving 100%
protection for up to 5 hours at a concentration of 5.0mg/
cm2
(Siriporn and Mayura, 2011).
Furthermore, Vatandoost and Vaziri (2004) also
reported that the mortality rate in Anopheles stephensi is
higher than Culex quinquefasciatus using A. indica leaf
extract.
Virendra et al., (2009) also recorded high
mortality in Anopheles stephensi followed by
Aedes aegypti and Culex quinquefasciatus using
A. indica oil. Application of the A. indica oil formulation
at the rate of 140mg/m2
in pit tanks and drains provided
above 90% reduction of Culex larvae up to one week
whereas 100% reduction was observed in Anopheles
larvae up to two weeks (Virendra et al., 2009). This is
more evident in our research findings too.
CONCLUSION
The extract is easy to prepare and it is a safe and
cheap natural product to be used to suppress mosquito
population. The early developmental stages are more
susceptible to the extracts than the later developmental
stages and since they (larvae and pupae) cluster at a
place, it is easier to kill and control than the adult stage
in which they disperse. Therefore, the use of plant
extracts especially Ocimum gratissimum in the control of
mosquito vector associated with human diseases is
highly recommended.
Ebe et al., 2014
077 Journal of Research in Animal Sciences (2014) 2(1): 068-078

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Journal of Research in Animal Sciences (2014) 2(1): 068-078 078
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