Insect-resistant transgenic crop plants have been obtained
through the introduction of Bacillus thuringiensis (Bt)
crystal protein genes (cry genes) in several species (Estruch
et al., 1997; Peferoen, 1992). Attempts have also been made
to produce insect-resistant transgenic plants through the
introduction and expression of foreign genes encoding
plant defensive proteins, such as protease inhibitors or
lectins, which showed anti-metabolic effects against certain
insects (Boulter et al., 1990; Hilder et al., 1987). Transgenic
plants which express Bt endotoxins or protease inhibitors
have been useful for control of insects which feed by
chewing plant tissues, such as species of the orders
Lepidoptera and Coleoptera, but have not been shown to
possess enhanced resistance towards sap-sucking insects
belonging to the order Homoptera.