Discussion
In the present study, field collected St . albopicta from
different parts of the Kerala with distinct breeding sites were
subjected to PCR amplification of WSP gene to determine the
prevalence of this intracellular bacteria and further amplified using
strain specific primers to confirm the strain. Also, selected amplified
sequences will then subjected to phylogenetic analysis.
The study revealed higher percentage of Wolbachia infection; 93%
of the 105 studied samples emphasizing the natural infection ofWolbachia in St . albopicta in Kerala, South India.
The two Wolbachia groups found were genetically distant and there
was no gene flow between wAlbA and wAlbB . RatherWolbachia in higher densities would cover the way for exploiting
this association for controlling vector mosquitoes of important
arboviral diseases. The study was aimed at identification ofWolbachia strains in field collected St. albopicta from
different breeding sites in Kerala. A total of 105 Samples were
collected from 3 different areas with different breeding sites, areca
nut planation in Kasaragod (North Kerala), rubber and pineapple
plantation in Kottayam (Central Kerala) and tyres and containers in
Thiruvananthapuram (South Kerala). The purified products were subjected
to PCR amplification (shown in Fig 3, 4, 5, 6, 7 and 8 ), usingWSP general primers (81F/ 691R). High prevalence and distribution
of Wolbachia strains are currently being reported from different
countries in Asian region including Korea and Malaysia (Park etal., 2016; Joanne et al., 2015). The importance of such
baseline studies play a vital role, mainly due to the initiative on
global campaign on eliminate dengue using Wolbachia as a
biological control measure (Eliminatedengue.com, 2016). Similarly in
India, studies in different states showed Wolbachia infection and
more recently a focus on natural infection with genotyping of its
strains in St. albopicta are reported (Park et al., 2016;
Joanne et al., 2015). However, an earlier report by Pidiyar
(2003) in Pune showed single infection with super group A forming a
separate group within wAlbA strain.
The present study focused on identification of Wolbachia strains
in St . albopicta from different breeding sites in Kerala.
The findings of this study concur with other published results showing
93% positive Wolbachia infection. The A and B superinfection
rate among positives sample was found to be 95%, and single strain
infection of wAlbA and wAlbB was 5% and 3% respectively.
Moreover, the negative or uninfected samples were recorded from
Thiruvananthapuram (4 samples) where major breeding sources, mostly man
made habitats. The samples may have been feeding from natural or
synthetic bactericide containing food source causing theWolbachia in them to perish in the wild. Besides, negative
samples may indicate maternal transmission leakage of Wolbachia(Park et al., 2016). Future studies should take this into
consideration specifically studies focused on prevalence ofWolbachia in an area. In addition five samples among 31 positive
samples from Thiruvananthapuram showed single infection withwAlbA strain; 16% within the study site samples. Similarly in
Kottayam 9% of the samples were singly infected with wAlbBstrain. Generally single infection points to incomplete cytoplasmic
incompatibility, Armbruster et al., 2003 conducted a study focused
on 18 different populations and found 100% positive infection ofWolbachia , hence more extensive sampling has to be conducted
within study sites before conclusions can be deciphered.
Phylogenetic analysis of Wolbachia strains based on the fast
evolving WSP gene showed that the prevalent Wolbachiaisolate was closely related with Wolbachia strains reported from
different geographical locations of India, such as Pune and Odisha (Daset al., 2014). Further analysis suggested that there was no
difference between the strains observed from the field collected
mosquitoes from different breeding sites, except for minor difference
from two sites having single infection; in Thiruvananthapuram and
Kottayam. The two strains belonging to group A and B, in St.
albopicta ; wAlbA and wAlbB respectively, were found to be
genetically distant (K2P=0.301) with no gene flow. There can be further
evolutionary strain within the groups.
Furthermore, evolutionary theory predicts that, due to maternal
inheritance, Wolbachia should evolve in a mutualistic fashion to
increase the fitness of infected females (Turelli, 1994). Overall the
effect of Wolbachia infection on insect fitness can be
mutualistic, parasitic or neutral, or even a combination. As forSt. albopicta , a laboratory studies of the mosquitoWolbachia -infected females lived longer and had more offspring
than their uninfected counterparts (Dobson et al., 2004, Dobsonet al. , 2002) but these benefits are offset by an increased rate
of death in infected larvae (Islam and Dobson, 2006). In addition
intraspecific transfer of Wolbachia strains into St.
albopicta was demonstrated by Xi et al., (2006) and these
strains as well as native strains in St. albopicta is
known to modulate arboviral infection specifically CHIKV (Moussonet al., 2012, 2010; Xi et al., 2006). Further, fewSt. aegypti samples; 20 were subjected to PCR amplification
using WSP general primers (81 forward and 691 reverse), to
determine if Wolbachia infection is present. But all the 20
samples including 8 males and 12 females were found to be uninfected
with Wolbachia.