Journal of Mosquito Research 2015, Vol.5, No.15, 1-15
2
products. However, in the past few decades a galaxy
of synthetic residual insecticides flooded the field of
public health and agriculture. Later with the
development of organophosphorus compounds, a new
era of insect and pest control began (Hassal, 1982).
Unfortunately, problems and backlashes have emerged;
indiscriminate use of insecticides in the control of
insect pests has led to resistance development by the
target species and also eliminated natural enemies.
Large quantities of four classes of insecticides viz.,
organochlorines, organophosphates and carbamates,
are applied annually to fields or indoors in China,
directly or indirectly bringing heavy selection pressure
on vector populations. One among the seven major
species of vector mosquito in China was
Ae. aegypti
wherein all have evolved resistance to all the above
types of insecticide except the carbamates (Feng et al.,
2006). The degree of resistance varies among mosquito
species, insecticide classes and regions. To overcome
such problems and in the background of the failure of
organochlorides and organophosphates in many foci,
search for new compounds have been undertaken
throughout the world. With the result, more safe and
degradable insecticides were realized by focusing on
pyrethroids, which constitute a new generation of
highly potent insecticides derived from a group of
esters. During 1980’s insecticides belonging to synthetic
pyrethroid groups were introduced in the public health
program in India. The pyrethrin was originally
extracted from the flower heads of
Chrysanthemum
cinerariaefolium
. Currently, these are important
weapons against insect pests of medical importance.
They show remarkably high toxicity and rapid action
against wide range of insects with relatively low
mammalian toxicity. In recent years, several new
pyrethroids are available with the structural rearrangement
of the stereochemical features of the parental ring.
They are recognized as nerve poisons that do not
interact with acetyl cholinesterase as organophosphates
and carbamates do. Synthetic pyrethroids are effective
as contact insecticides and to a lesser extent as
stomach poisons as well (Mulla et al., 1980). The
larvicidal effects of the pyrethroid have been
extensively evaluated on various mosquito species
including dengue vectors (Ranvanshi et al., 1982;
Verma et al., 1983). The action of pyrethroids on
insects, and mammals depends on the optical and
geometrical configurations of their acidic and alcoholic
compounds. In the natural pyrethrum all the esters are
present in most active optical and geometric
configurations as against the commercial pyrethroids
where two or four or eight isomers are found (Elliot &
Janes, 1973). Inspite of the said qualities, many
authors have reported development of resistance
against pyrethroids as well (Chandre et al., 1988;
Ponlawat et al., 2005). Hence, it has become essential to
test the pyrethroid susceptibility status of vector
populations in different foci.
The susceptibility status of an insect population to any
insecticide depends on several factors such as the
genetic constitution, ecology of breeding place,
previous history of insecticide application if any in
that area and the cross resistance spectra. Recent study
in African continent indicated that the extensive use of
pyrethroid insecticides in malaria vector control has
increased dramatically in the past decade through the
scale up of insecticide treated net distribution programmes
and indoor residual spraying campaigns. Inevitably,
the major dengue and malaria vectors have developed
resistance to these insecticides and the resistance
alleles are spreading at an exceptionally rapid rate
throughout Africa (Hilary et al., 2011). In view of the
frequent outbreaks of dengue in different parts of the
country (India), including Karnataka state, it is felt
essential to generate a base line data on the susceptibility
of vectors of local importance.
Even today, Liquid formulations of pyrethroids are
extensively used in households; especially in urban
and city limits to protect themselves from mosquito
bites, through repellent, knockdown and killing effects
(Jaswanth et al., 2002). However, prolonged exposure
to these chemicals due their long term persistence,
high toxicity and propensity for accumulation may
lead to the development of resistance in the insect
populations, and cause resurgence of minor or
alternative pests/vectors, creating ecological disasters
(Sharma et al., 1992).
A large number of studies have shown that multiple,
complex resistance mechanisms in particular, increased
metabolic detoxification of insecticides and decreased
sensitivity of the target proteins or genes are likely
responsible for insecticide resistance (Nannan Liu,
2015). Resistance/tolerance to insecticides can be
defined as an inherent ability to tolerate dosage of an
