Journal of Mosquito Research 2015, Vol.5, No.15, 1-15
12
detect resistance levels considering some important
detoxifying enzymes as targets. On the other hand, as
different isozymes are inherited co-dominantly at
individual loci, it is possible to detect the genotype of
an individual from the electrophoretic profile.
Therefore, it has become apparent that such techniques
hold considerable promise in relating specific target
enzyme to resistant genotypes rather than phenotypes
in a single insect.
Esterases can be divided into carboxylesterase (CaE)
and acetyl cholinesterase (AChE), the former is
involved in detoxification of organophosphates and
pyrethroids. In the present investigation, the results of
Spectrophotometric analysis of Est-A (Figure 7) and
Est-B (Figure 8) have revealed that in
Ae.
aegypti
–
rural larvae, there was more activity than that of urban
(Table 5). An elevation of non-specific esterases
associated with deltamethrin resistance in four out of
five field populations of
Ae. aegypti
from Thailand
when compared to susceptible strain (Yaicharoen
et al
.,
2005). Similarly In eastern Uganda
Anopheles gambiae
adults were exposed to WHO discriminating
concentrations of DDT, permethrin, deltamethrin,
bendiocarb and malathion. Survival rates to DDT were
as high as 85.4%, alongside significant resistance
levels to permethrin (38.5%), reduced susceptibility to
deltamethrin, but full susceptibility to bendiocarb and
malathion (Urvashi et al., 2009).
The quantitative estimation studies on AcPH of
Ae.
aegypti
larvae have revealed that in rural population
there was more activity than that of urban (Figure 10).
APH also shows enhanced activity in rural larvae than
that in urban larvae (Figure 11). As phosphatases are
involved in breakdown of P-S bonds containing
insecticides, significantly higher level of phosphatases
in rural populations especially in Nanjangud populations
can be correlated with relatively more pyrethroid
tolerance noticed (Table 5). Similarly elevated level of
Phosphatases was observed in
Helicoverpa armigera
an important cotton pest at Gulbarga, India (Srinivas
et al., 2003).
Spectrophotometric analysis of G6PD enzyme of
Ae.
aegypti
(Table 5) has registered significant difference
in activity in populations from urban and rural area
(Figure 9). Thus,
Ae.
aegypti
has shown more activity
in rural populations especially in Channarayapatna
and Mandya populations compared to urban
population. The differences in the G6PD activity in
normal and treated lines were also noticed earlier
(Ganesh et al., 2002; Urmila et al., 2001; Kumar et al.,
1991). Thus the higher tolerance level in rural population
may be due to more activity of the G6PD enzyme.
In the present investigation a total of five enzymes,
which have direct or indirect role in overall fitness
were studied. The overall result indicates that all the
three groups (I, II & III) of enzymes may have certain
role in conferring relatively more fitness in terms of
tolerance to insecticide tested in
Ae.
aegypti
, rural
populations. This reiterates the idea that biochemical
approach for the detection of insecticide resistance/
tolerance will help us in Integrated Vector Management
(IVM) in rural areas, where these species might have
an earlier exposure to agricultural insecticides. The
overall profiles of isozyme studies also indicate that,
out of five enzyme loci examined in two populations
of
Ae.
aegypti
, the isozymes of Est-A (Figure 2, Table
2) and Est-B (Figure 3, Table 3) have revealed
significant variation in the allelic frequency. On the
other hand, certain alleles could be seen only in one
population and absent in the other. In addition,
monomorphism was found for
Ae.
aegypti
- AcPH
(Figure 5) and APH (Figure 6) enzymes (Table 4). In
the present study susceptibility status of urban
populations and Resistance ability of vector in rural
populations of Mysore and surrounding areas are
biochemically studied quantitatively in addition to
qualitative assay’s and are documented in order to aid
the researchers in designing novel potent molecules
that are safe to mammals and have more target
specific to the vectors in future vector management
strategy.
4 Conclusions
The knowledge on diversity, systematics with a base
line data on susceptibility to insecticides along with
their biochemical genetics will be helpful while
undertaking any control measures in future in rural
areas. Identification of resistance mechanisms will be
helpful to reveal the cross-resistance spectrum facilitating
the choice of alternative insecticides and allows
monitoring of foci with endemicity. So these two
populations of
Ae.
aegypti
from urban and rural
habitats have presented differential isozyme profile
