|Zhu, Kun yan|
Submitted to: Biopesticides International
Publication Type: Review article
Publication Acceptance Date: 1/31/2008
Publication Date: N/A
Citation: Interpretive Summary: Transgenic corn expressing Bacillus thuringeinsis (Bt) toxins has been planted to control the European corn borer. Over the past 20 years, research has been ongoing to understand Bt resistance in corn borer populations. Overall, the data suggest that resistance is linked to alterations in digestive enzymes in some corn borer larvae. However, these larvae are unable to survive on transgenic corn. These results demonstrate that these transgenic corn varieties expressing Bt toxins are effective in controlling susceptible and resistant populations of corn borers.
Technical Abstract: The European corn borer, Ostrinia nubilalis (Hübner), is the primary target of the widely adopted transgenic corn events MON810 and Bt11, expressing the Bacillus thuringiensis (Bt) insecticidal toxin, Cry1Ab. Resistant strains of O. nubilalis have been selected in the laboratory by exposure to Bt toxins. The physiological changes in resistant O. nubilalis have been thoroughly studied, particularly in a Dipel-selected strain from Kansas corn fields, KS-SC. Resistance to Cry1Ab and Cry1Ac protoxins in KS-SC was not associated with receptor binding, but was attributed primarily to reduced protoxin activation due to down regulated expression of at least one trypsin gene in the gut of resistant larvae. Proteinase-mediated resistance in this strain was ineffective against trypsin-activated Cry1Ab toxin or Bt transgenic corn, even though MON810 and Bt11 events express an incompletely-activated truncated form of Cry1Ab. Therefore, KS-SC larvae responded to plant-derived Cry1Ab toxin as though they were fed functionally activated toxin. These observations may be explained by experiments that determined that transgenic Cry1Ab expressed in planta can be hydrolyzed by plant enzymes in corn leaf extracts to a form similar to trypsin-activated Cry1Ab. The data indicate that resistant insect populations with reduced proteinase activity are not able to challenge the efficacy of these transgenic crops.