In nature, many strategies are used by plants to
protect themselves against insects [55]. Various
secondary metabolites are toxic to insects, but their
biosynthetic pathways are rarely known or too
complex for them to be used to create insect-resistant
plants [71]. This fact explains the use of
proteins, such as B. thuringiensis toxins, that are
encoded by a single gene. Moreover, the molecule
that is expressed has to remain active after ingestion
of the plant tissues by the insect. Continuing
research on new sources of resistance is essential
for the long term control of insect pests. In a first
step, studies on the expression and potential of the
new insecticidal genes can be performed in model
plants such as tobacco and Arabidopsis thaliana, as
recently proposed by Santos et al. [72]. In a second
step, the selected gene(s) must be introduced into
the target crop. Very often, transformation procedures
work with cultivars which are not elite
commercial varieties and therefore, when a transformation
event has been shown to improve the
efficacy of insect control, a backcrossing process
must take place. In another step, field trials must
be performed in different locations and for several
years to demonstrate that the characteristics of the
new lines are identical to that of the original elite
cultivar. These different steps explain why the
development of insect-resistant crops is a long term
process, and why these programs are mainly developed in private companies in industrialized countries.
Part of the contribution of transgenic crops
to a safer and more environmentally friendly crop
protection system will be taking place in developing
countries where crops (cotton and rice for
example) requiring high insecticidal treatments are
grown. However, the introduction of insect-resistant
crops must be accompanied by a resistance
management strategy and, even without taking
regulatory issues and intellectual property rights
(which are not the aims of this review) in consideration,
the delivery of this new technology to these
countries will be more challenging. Another factor
affecting the future of these crops is the public
acceptance of products derived from transgenic
plants. Better consumer information is necessary to
allow a well-informed decision based on the comparison
of the potential benefits of transgenic
plants with the reliance on chemical insecticides.