The simultaneous introduction of three genes
expressing insecticidal proteins (Cry1Ac, Cry2A, and
Gna) into rice to control three major pests (rice leaf
folder, yellow stemborer and the brown planthopper)
imparted more resistance than combinations of only
two of these transgenes (Bano-Maqbool et al. 2001).
Another study of transgene pyramiding showed that
transgenic cotton containing two Bt genes (Cry1Ac
and Cry2Ab) performed better than the single gene
Cry1Ac or the Cry2Ab transgenic cotton (Jackson et
al. 2004).