Which insect genes should be targeted? The screening
approach used by Baum et al. has already identified a
series of potential targets in corn rootworm, of which a
gene encoding the b-subunit of a COPI coatomer complex
was the most effective in terms of LC50 for RNAi in
artificial diet. The COPI complex is involved in translocation
of proteins from endosomes to the cytoplasm, as well
as other potential roles in protein trafficking in the cell, but
it is not obvious why interference with this function should
be lethal. The screening approach can thus identify targets
that would not necessarily be predicted from functional
considerations but has the drawback of being very labourintensive
if large numbers of insect bioassays are required.
However, the demonstrated efficacy of targeting V-type
ATPase A could easily be extended to other insect species.
The approach of Mao et al., in which insect detoxification
mechanisms towards plant secondary metabolites are targeted,
has the advantage of being predictable and specific
to pests that feed on a crop producing a defined defensive
chemical [48,49]. It can be readily extended to detoxification
mechanisms in other plant–insect interactions.
Further development of RNAi biotechnology could also
seek to complement existing crop protection strategies;
for example it might be possible to use technologies in
combination to counter broad-range, protein-degradationbased
resistance to Bt toxins (observed in highly polyphagous
insect pests such as Heliothis virescens, which gain
resistance through the upregulation of specific proteinase
genes [50]).