RNAi-mediated gene knockdown in Drosophila is localised
to the site of dsRNA delivery and effects are temporally
limited; indeed, a systemic long-lasting RNAi response has
never been observed in Drosophila, in contrast to C. elegans
[1]. The systemic RNAi effect in C. elegans is a multistep
process that requires the amplification and spread of
the silencing signal [11,14]. If a similar system was present
in insect pests, it would enable targets to be selected from
the whole insect (not just gut-specific targets). In addition,
the RNAi amplification step would negate the need for a
continuous supply of high levels of dsRNA, and thus could
avoid many of the problems associated with the instability
of dsRNA in the insect gut.