The pestiferous and non-pestiferous (Clarke et al 2005).

The Bactrocera dorsalis (Hendel) also known as the oriental fruit fly
is a notorious pest of fruit crops and vegetables in India and whole of the
South East Asia. It belongs to the Dacinae subfamily of the family Tephritidae.
India has reported to have 5% of the Tephritid fauna of the world, nearly 200
fruit flies of which the B. dorsalis, B.
zonata (Saunders) and B. correcta are economically
significant (Vergese 2002). In
South East Asia B. dorsalis occurs as
a complex of fruit flies consisting of several morphologically similar species
both pestiferous and non-pestiferous (Clarke et al 2005). It is a polyphagous pest having
a wide host range infesting around 117 species (Allwood et al 1999). It is distributed throughout India and active all the
year, except in north India where it hibernates during winter. In Punjab, B. dorsalis and B. zonata are the predominant fruit fly species reported to infest
guava, mango, citrus, peach, ber, pear, plum, loquat, sapota, fig and jamun. Guava
is considered as the second most important fruit
crop in Punjab (Anonymous 2016) while it also serves as the most common
host for fruit flies of B. dorsalis complex
(Clarke et al 2005). The oriental
fruit fly causes economic loss of 10-80% in guava (Vergese 2002) and even up to
100% damage during rainy season (Singh 2012, Singh and Kaur 2016). Considering
these losses by this pest, it is now being looked upon as a national concern.

The adult female fruit fly
oviposits on mature fruits, laying eggs in the soft epicarp region of guava and
thus, it’s a serious quarantine pest throughout world. The maggot hatches and
feed on the edible portion of the fruit, eventually leading to the decay and
fall of fruits. These maggots then pupate in the soil up to the next favorable
conditions. After emergence of adult fruit flies, these feed upon the nectar
from flowers of fruit crop present in the field during that time (i.e. guava).
The management of this pest has become difficult because of its polyphagous
nature and unexposed developmental stages (Sharma et al 2011). Integrated pest management consisting of a combination
of management techniques rather than a single method has proven to be more
efficient in reducing the infestation in mango (Vergese 2002). The conventional
practices already in use are facing limitations like development of resistance
by insect pests against pesticides, broad spectrum activity of pesticides
affecting non-target organisms, and limitations of pheromone based fruit fly
trap like insufficient supply
and short lasting effects of pheromone in field. Thus, often a single approach is not sufficient to tackle
fruit fly and it necessitates collective management practices. However,
continual review and development of the established methods are of prime importance
to maintain their efficacy. Which is why development of novel strategies are of
prime importance. These factors now have necessitated the modern
biotechnological interventions in pest control which could rule out the above
said shortcomings. This purpose can very well be served by RNA interference
(RNAi)-mediated gene silencing. RNAi is a highly specific and reliable method
which can be employed for targeting important genes of fruit fly required for
its survival, growth and reproduction. The sequence specific action of this
method could be a great promise for effective pest management. This method is
already being used to develop various pest and disease control strategies (Duan et al 2012, Joga
et al 2016, Mamta
and Rajam 2017, Darrington et al 2017).
It requires the potential target gene of pest and efficient dsRNA delivery
method. This technique is still under development, has many areas to explore
and there has been no work of developing RNAi-mediated pest control strategies
in India against fruit fly.

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 RNAi is a post-transcriptional, sequence
specific suppression of gene expression in eukaryotes. Several candidate genes of B. dorsalis such as rpl19, a ribosomal protein, Noa,
fatty acid elongase, v-ATPase-D subunit and Rab11, a GTPase have been utilized for double-stranded RNA (dsRNA)-mediated
gene silencing (Li et al 2011). Earlier,
genes involved in sex-determination of fruit fly has also been proposed
for developing new genetic control strategies (Raphael et al 2004). The double sex gene (dsx) is the bottommost gene involved in the sexual-determination
hierarchy (Wilkins 1995). This is unique and highly
conserved, acts as a switch between upstream regulators and downstream sexual
differentiation by acting as a transcriptional factor of the downstream genes
determining the sexual dimorphism (Chen et al 2008, Permpoon et al 2010).
The gene produces two isoforms of mRNA i.e. male and female specific which
produces DSXM and DSXF proteins respectively (Baker and Wolfner 1988, Burtis
and Baker 1989) that control the sexual differentiation in all insects. Due to the utmost importance in sexual
determination, evolutionarily conserved nature and differential action specific
to the different sexes, this gene poses great potential to be exploited for
pest control strategies.
It has been well characterized in Drosophila and the effect of injection of
dsRNA of dsxf gene has been
studied in B. dorsalis (Chen et al 2008). Yet
there is no clear understanding of the differential action of its protein
isoforms in both the sexes. Hence, by this study we aim to understand the
silencing effects of dsx in both male
and female fruit flies for its management in field.