Journal of Mosquito Research 2015, Vol.5, No.15, 1-15
11
area of
Aedes aegypti
species, isozyme profile and
enzyme activity studies were carried out.
Esterases, Dehydrogenases and Phosphatases are
standard metabolic enzymes which are studied by
Native PAGE to gain insight into the species as well
as strain variations in mosquitoes. Esterases are
complex enzymes acting on a variety of substrates and
are capable of hydrolyzing ester bonds. On the other
hand Phosphatases work on a limited type of
substrates where they will either add or remove the
phosphate group. In Dehydrogenases, the reduced
NADP or NADPH formed during the reaction passes
electrons through an intermediate electron carrier,
usually phenozine methosulphate to a tetrazolium
compound, resulting in the formation of an insoluble
purple diformazen dye at the site of the enzyme
activity. In the present study, three types of enzymes
viz., Esterases, Phosphatases and Dehydrogenases
were employed. These enzymes can be grouped into
Group I, Group II and Group III based on their activity.
The data obtained has revealed more poplymorphism
in esterases in constrast to group II and group III
enzymes which are less polymorphic. This also shows
that Esterases are highly changeable in nature as
evident from the present study on both the populations
of
Ae.
aegypti
.
Phosphatases are highly active and stable hydrolytic
enzymes, used in immunological assay as a label. It is
also an excellent marker with potentially useful
applications in assessment of variability in natural
population (Sakai et al., 1973). These are also
responsible for the breakdown of P-S bonds of the
insecticides (Callaghan, 1991). Organophosphates,
Carbamates and Pyrethroids contain carboxylester and
phosphotriester bonds that are subject to attack by
enzymes. In addition, Phosphatases are also involved
in metamorphic events in insects. In the present study,
the populations of
Ae.
aegypti
from both urban and
rural area have shown one allele for AcPH (Figure 5),
so the frequency of the two alleles between the
populations was insignificant (P>0.05). In contrast
Igbokwe & Milles (1982) have compared 5 inbred
strains of
Ae.
aegypti
for APH and AcPH and found 7
and 4 bands respectively at Venezuela.
The allelic frequency of the third group of enzymes
observed
i.e.,
dehydrogenase (G6PD) (Table 4) for
Ae.
aegypti
along with its allelomorphs (Figure 4) of
urban and rural populations. G6PD is a NADPH
generating enzyme involved in redox reaction. The
NADPH generated by G6PD is utilized by
monooxygenases. Cytochrome dependent monooxygenases
are extremely important metabolic system involved in
catabolism and anabolism of xenobiotics and
endogenous compound. Monooxygenase mediated
detoxification is a common mechanism by which
insects become resistant to insecticides. Thus increase
in the monooxygenase activity must be reflected in
G6PD activity also (Kumar et al., 1991). In the
present study, G6PD enzyme has shown variability
between the populations of
Ae.
aegypti
from urban
and rural habitats (Figure 9). The rural population has
revealed three bands G6PD
0.9, 1.00 and 1.05
in contrast to
only one in urban population (Figure 4). Kumar et al.,
(1991) could get only two G6PD isozyme bands each
for
An.
stephensi
,
Ae.
aegypti
and
Cx.
quinquefasciatus
Delhi, India. Pushpalatha & Vijayan (1999); have
studied the isozyme patterns of G6PD of two culicine
mosquitoes namely
Cx.
vishnui
and
Cx.
fuscocephala
from Mysore, and could find two bands each in both
the species. However, the study of Fakoorziba (2005);
revealed that
Cx.
tritaeniorhynchus
variant (type B) at
Mysore polymorphic with 3 alleles compared to only
one allele (monomorphic) in another type A. The
present study reveals that the rural populations of the
species are polymorphic with 3 alleles each when
compared to only one allele in urban populations
(Figure 4).
For decades, field studies on resistance problems
insitu
have relied on the WHO bioassay kit. Although
much has been learned from these detection systems,
it has several inherent limitations. Only one insecticide
can be tested per insect without a known discriminating
dose, large number of insects is needed to generate
probit lines. Using this method, determination of the
resistance level or mechanism is not possible.
Moreover discriminating dosage that could be applied
to all mosquitoes does not exist. Also false positive
may occur because of deteriorating filter papers of
procedural variables, such as temperature or humidity.
Finally, the bioassay methods are ineffective in
detecting resistance phenotypes at low frequency
(Brogdon et al., 1988). For these reasons, development of
quantitative techniques such as spectrophotometric
and microtitre plate assay are being used nowadays to
