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Screening of Local Plants for Their Repellent Activity against Mosquitoes (Diptera: Culicidae)
100
Thangam and Kathiresan, 1992). Pandian et al. (1989)
observed the repellent activity of herbal smoke on the
biting activity of
Culex
quinquefasciatus
. Thangam
and Kathiresan (1992) stated that smoke from burning
various dry materials has been used since early times
to deter insects especially mosquitoes. Hwang et al.
(1985) observed that the bundles of dried
Artemisia
vulgaris
were burned to repel biting insects since it
contains insect repellents that can be released from the
plant by combustion. The smoke of the leaves of
Vitex
negundo
and
Leucas
aspera
were found more toxic to
the filarial vector mosquito,
Culex
quinquefasciatus
than the synthetic mosquito mats which contain 4%
d-allethrin (Pandian et al., 1994).
Anopheles
karwari
was repelled by coconut husks, ginger and betel nut
leaves. Culicines were repelled by mango wood,
coconut husks, ginger and beetle nut leaves (Vernede
and Marnix, 1994).
The repellent activity of plants might be due to the
presence of certain chemicals that are able to irritate the
olfactory senses of the mosquitoes. These chemicals
can be grouped into three major categories
viz
.,
alkaloids, phenolics and terpenoids. Alkaloids are
basically insecticidal at low concentration,
nevertheless they can be used as a repellence. They are
non volatile and release insecticidal smoke when the
plant materials or the mosquito coil containing the
active ingredients are burnt. They repel the mosquitoes
through direct toxicity (Sears, 1996). Mosquito
repellent chemicals present in the plant contain
phytochemicals like, methone, limonene, beta pinene,
alpha pinene and linaliol (Eun, 2001). Burning wood
and adding repellent plants to it probably works in
several ways. First, the smoke may disguise human
kairomones and disrupts convention currents essential
in mosquito host location. Secondly, burning may,
release repellent irritant molecules and the molecules
released by the plants also may be insecticidal
(Charlwood and Jolley, 1984). Therefore, the use of
plants in mosquito control is an alternative pest
control method for minimizing the noxious effects of
some pesticidal compounds on the environment
(Fatope et al., 1993). Botanicals have widespread
insecticidal properties and will obviously work as a
new weapon, and in future may act as suitable
alternative product to fight against vector mosquitoes
(Ghosh, 2012). It may conclude that natural products
from plants of insecticidal and medicinal values have
higher efficiency in reducing mosquito menace due to
their repellent toxicity. Further in-depth laboratory
studies and field bioassays are needed as the present
study indicated that there is scope to use local plants
to control and repel mosquitoes
.
3 Material and Methods
3.1 Collection of plants
Five plants
viz
.,
Azadirachta indica, Citrus medica
,
Murraya koenigii, Ocimum tenuifloreum
and
Ricinus
communis
were collected in and around Tambaram,
Chennai, Tamil Nadu, India. The plants were selected
based on available literature, abundant availability,
medicinal and insecticidal properties. The details of
collected plants utilized for the present study are
presented in Table 2. The collected plant leaves were
brought to the laboratory, washed with dechlorinated
water, shade dried under room temperature and was
then powdered individually.
3.2 Bioassay
Powdered plant parts burned on glowing charcoal
produce smoke acts as a repellent mosquitocide
(Kazembe and Nkomo, 2010). In the present study, the
same methodology was adopted. The repellent activity
was studied under natural conditions in the field. Field
observations were undertaken in Meenakshi Avenue,
Old Perungaluthur, Chennai, Tamil Nadu, India based
on the assessment of mosquito density status in the
natural/domestic habitats during dusk which involved
direct observations. A total of six houses were selected
of which four were used for treatment. The house
treated with burning of charcoal only served as
negative control and the other house as positive
control did not receive any treatment including
charcoal. In each of the four houses selected for
treatment, the dried powdered leaves of each plant
(250g) were burnt on glowing charcoal. The burning
of five plant leaves was changed in a cyclic manner to
avoid bias during each trial. A total of five trials were
carried out. The experimental set up was kept out of
reach of children and use of mosquito repellents was
discouraged during the period of study. Prior to the start