Contents - Faperta

Deployment of Insect-Resistant Transgenic Crops for Pest Management 331
(Kaiser, 1996). Similarly, H. armigera and H. punctigera destroyed the cotton crop in the
second half of the crop-growing season in Australia because of reduced production of
Bt toxins in the transgenic crops (Hilder and Boulter, 1999). Possible causes for the failure
of insect control may be due to: (1) inadequate production of the toxin, (2) effect of the
environment on expression of the transgene, (3) locally resistant insect populations, and
(4) development of resistance due to inadequate management.
A cotton crop fl ooded with 3 to 4 cm deep water for 12 days lost resistance to insects
signifi cantly compared with the control plants irrigated normally (Y.R. Wu et al., 1997). A
similar reaction has been observed in Bt cotton, which grew in overcast and rainy weather
continuously for 21 days. When the water logging was over, the cotton plants recovered
gradually and their insect resistance increased to some extent. Under fl ooded conditions,
the activity of superoxide dismutase increased considerably in Bt cotton plants at fi rst, and
then dropped continuously. Epistatic and environmental effects on foreign gene expression
could infl uence the stability, effi cacy, and durability (Sachs et al., 1996). CryIA gene
expression is variable and is infl uenced by genetic and environmental factors. The CryIA
phenotype segregates as a simple, dominant Mendelian trait. However, non-Mendelian
segregation occurred in some lines derived from MON 249. Expression of transgene is
infl uenced by: (1) site of gene insertion, (2) gene construct, (3) epistasis, (4) somaclonal
mutations, and (5) physical environment. Appropriate evaluation and selection procedures
should be used in a breeding program to develop crop varieties with stable expression of
the transgene.
Conclusions
Incorporation of insecticidal genes in crop plants will have a tremendous effect on pest management.
Emphasis should be placed on combining exotic genes with conventional host
plant resistance, and also with traits conferring resistance to other insect pests and diseases
of importance in the target region. Although several crops with commercial viability have
been transformed in the developed world, very little has been done to use this technology
to develop insect-resistant cultivars to increase food production in the harsh environments
of the tropics. There is a need to follow integrated pest management (IPM) practices to make
transgenic crops a viable technology for pest control. Emphasis should be given to commercial
and regulatory requirements for the deployment of transgenic crops, including spatial
and temporal expression of the transgene, and food and feed safety of the product.
References
Alinia, F., Ghareyazie, B., Rubia, L., Bennett, J. and Cohen, M.B. (2000). Effect of plant age, larval age,
and fertilizer treatment on resistance of a cry1Ab-transformed aromatic rice to lepidopterous
stem borers and foliage feeders. Journal of Economic Entomology 93: 484–493.
All, J.N. and Treacy, M.F. (1997). Improved control of Heliothis virescens and Helicoverpa zea with a
recombinant form of Autographa californica nuclear polyhedrosis virus and interaction with
Bollgard R cotton. In Proceedings, Beltwide Cotton Conference, 6–10 January, 1997, New Orleans,
vol. 2. Memphis, Tennessee, USA: National Cotton Council, 1294–1296.