author(s)
R Gopalakrishnan, S Subramanian and Vinay Kalia

abstract
RNA interference (RNAi) is a gene silencing mechanism mediated by double-stranded RNA (dsRNA) through post-transcriptional regulation. RNAi is capitalized for studying gene function in a variety of organisms and it is commonly employed for down regulating gene expression in cell. The principle of RNAi silencing involves custom steps such as processing of dsRNA, formation of RNA-induced silencing complex (RISC), target mRNA binding and cleavage. Nucleolytic degradation of the besieged mRNA by the RNase I enzyme (Argonaute - in case of insects) and RNase H enzyme (slicer - in case of nematode) results in gene silencing. The dsRNA uptake mechanism is mediated either through transmembrane channel or through endocytosis in insects. Among them SID-1 protein with 4 transmembrane domains is the major portal site for dsRNA uptake in insect midgut ^[15]. RNAi was successfully established in several insect orders like Coleoptera, Orthoptera, Diptera, Hemiptera and Lepidopteran pests such as corn planthopper, whitefly and pea aphid ^[51]. RNAi was highly efficient in coleopteran insects and have very low efficient in lepidopteran insects and the range of efficiency varies from 40% to 90% in insects. The variation is due to the inherent difference in RNAi machinery in insects influenced by different factors such as RNase, RNA-dependent polymerase (RdRP), SID 1 transmembrane channels and gut pH ^[32]. The presence of RNA nuclease (RNase) in the midgut and absence of RdRP in insects results in degradation of dsRNA in insect and trapping of dsRNA in acidic bodies in the midgut cells yields poor RNAi response in lepidopteran insects ^[45]. Understanding the inherent difference in RNAi machinery will help to resolve the strategies for efficient pest management through RNAi.