202 R. Asokan et al.
entomology. In the year 2007 two research
groups from China and USA experimentally
validated the utility of RNAi in insect pest man-
agement. The choice of the gene for RNAi medi-
ated silencing could be many and generally falls
into two broad categories, viz. silencing of genes
that results in quick control, for example, genes
involved in insect–plant interactions, digestion,
moulting, etc. and silencing of genes that results
in long-term management, for example, genes
involved in pheromone biosynthesis, pheromone
reception, migration, flight, diapause, etc. Mao
et al. ( 2007 ) demonstrated that it is possible for
a no chemical management of the cotton boll
worm, Helicovera armigera Hub. by transgenic
cotton mediated silencing of cytochrome P 450.
Similarly Baum et al. ( 2007 ) proved that RNAi’s
approach is feasible in the management of the
coleopteran pest the corn root worm ( Diabrotica
virgifera virgifera LeConte).
Plant Mediated-RNAi Against
Insect Pests
The discovery of RNA interference was first
studied in Caenorhabditis elegans where soak-
ing of nematode in dsRNA solution resulted in
the degradation of the target mRNA and thus
affected the protein synthesis. So far more than
32 target genes have been screened for their po-
tential for gene silencing in insects (Zhang et al.
2013 ). These observations showed that RNAi re-
sponse in several less derived species is robust
and inheritable (Ronco et al. 2008 ), whereas, it is
otherwise in more derived species, for example,
Lepidoptera exhibits variable RNAi response
when administered with exogenous dsRNA
(Terenius et al. 2011 ). The tremendous success of
RNAi facilitated plant biotechnologists to utilize
the various physiologically important genes from
insects as ingestible insecticides through plant
mediated expression of cognate dsRNA. The era
of plant mediated RNAi (PM-RNAi) is a new line
of defense against insects and nematodes (Huang
et al. 2006 ; Baum et al. 2007 ; Mao et al. ( 2007 ).
Potential of PMRNAi in the management of
root knot nematode (RKN) was successfully dem-
onstrated by Huang et al. ( 2006 ), in Meloidogyne
incognita L. In vitro studies revealed that a full
length dsRNA16D10 reduced 93–97 % of tran-
script and 16D10 peptide by 65–69 % and re-
duced the extent of gall formation. Similarly
Baum et al. ( 2007 ), studied 290 genes from West-
ern corn root worm, Diabrotica virgifera virgefer
and 14 genes like V-ATPase A, D, E and α-tubulin
showed immediate response within 24 h of ap-
plication of dsRNA. Similarly, susceptibility of
other coleopterans such as Southern corn root-
worm, Diabrotica undecimpunctata; Colorado
potato beetle, Leptinotarsa decemlineata Say and
cotton boll weevil, and Anthonomus grandis Bo-
heman were studied for their response to RNAi.
Recently dsRNA for Mi-Rpn7 of M, incognita
was introduced into the soyabean through hairy
root culture for managing plant parasitic nema-
todes (Niu et al. 2012 ). The PMRNAi has been
efficiently utilized in the control of green peach
aphid Myzus persicae Sulzer which transmits
more than 100 type of plant viruses by silenc-
ing Rack1 ( Receptor of Activated Kinase C) and
C002 genes (Pitino et al. 2011 ). Rack1 based on
the earlier gene silencing results as carried in the
C. elegans (Simmer et al. 2003 ; Kamath et al.
2003 ) and Heterorhabditis bacteriophora Poinar
(Ciche et al. 2007 ). Where knock down of this
gene in M. persicae resulted in lethality in early
developmental stage, stunted growth, reduced
egg laying etc. Rack1 is the multifunctional re-
ceptor protein and one of the internal compo-
nents of the circadian clock binds to the various
proteins and initiates signal transduction cas-
cades, it also functions in the actin organization.
Another target gene of M. persicae was MpC002
a homologue of COO2 that plays an important
role in insect–plant interaction and is expressed
predominantly in salivary glands. Knockdown
COO2 gene resulted in mortality and improved
tolerance to peach aphid in transgenic tobacco
plants.
Similarly, Mao et al. ( 2007 ) successfully
silenced the allelochemical, gossypol detoxifying
gene of H. armigea through artificial diet con-
taining dsRNA for CYP450 monooxygenease
gene and developing dsRNA expressing trans-
genic plants where there was two-fold weight