Unfortunately, profound troubles are appearing in the use of commercialized Bacillus thuringiensis transgenic crops. Duration and concentration of Bt toxin are not proper in many Bt cotton varieties in India, thus supplementary chemical control is needed because Cry1Ac toxin quantity at various foliar levels decreases during the growing season.
Kranthi, K.R., Naidu, S., Dhawad, C.S., Tatwawadi, A., Mate, K., Patil, E., Bharose, A.A., Behere, G.T., Wadaskar, R.M. and Kranthi, S. (2005): Temporal and intra-plant variability of Cry1Ac expression in the Bt-cotton and its influence on the survival of the cotton bollworm, Helicoverpa armigera (Hübner) (Noctuidae: Lepidoptera). Current Science 89: 291-298.
Another trouble is – as a consequence of the continual use of Bt transgenic cotton in China, India and also in other countries – the increase of pest species from the family Miridae which cannot be controlled by Bt toxin. Thus, growers were to apply chemical insecticides making the growing of Bt cotton more expensive than that of the so-called traditional technologies using exclusively synthetic insecticides.
Pearson, H. (2006): Transgenic cotton drives insect boom. Secondary pests could undermine initial benefits of Bt cotton. http://www.nature.com/news/2006/060724/full/060724-5.html
Lu, Y., Wu, K., Jiang, Y., Xia, B., Li, P., Feng, H., Wyckhuys, K.A.G., Guo, Y. (2010): Mirid bug outbreaks in multiple crops correlated with wide-scale adoption of Bt cotton in China. Science 328: 1151-1154.
Considering maize varieties which contain Bt toxin gen, there were difficulties in explaining control failures before the scientifically proved finding of Bt toxin resistant Diabrotica virgifera population in the United States.
Gassmann, A.J., Petzold-Maxwell, J.L., Keweshan, R.S., Dunbar, M.W.(2011) Field-evolved resistance to Bt maize by Western Corn Rootworm. PLoS ONE 6(7): e22629. doi:10.1371/journal.pone.0022629
Gray, M. and Staffey, K. (2004): Transgenic corn rootworm hybrid stumbles in Urbana experiment; some producers also report severe lodging with YieldGard Rootworm hybrid in commercial fields. IPM Bulletin, University of Illinois No. 22. 1-6. http://www.univ.edu./bulletin/print.php?id=181
I would like you to display your own experiences with a bit of explanation of the possible reasons.
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