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Sensitivity of Lepidopterous Larvae to Recombinant Products of Bacillus thuringiensis as a Bioinsecticide Agent

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Author(s): K.A. Zaied | Z.M. El-Diasty | Kawther S. Kash | M.E. Ismail

Journal: Pakistan Journal of Biological Sciences
ISSN 1028-8880

Volume: 6;
Issue: 3;
Start page: 273;
Date: 2003;
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ABSTRACT
The present study was conducted on sensitivity of transgenic bacteria that express one or a few toxins from Bacillus thuringiensis (Bt) were obtained in this study through conjugation between different eight Bt strains from different serovars agent. Products from 28 transconjugants were screened for larvicidal activity against S. littoralis, containing naturally occurring combinations of spores and crystal proteins, as well as, each of one product alone. Bt products containing cry + end from some transconjugants resulting significant mortalities over their mid-parents in the second and fourth instars of F1 generation attributed to synergistic interactions. In the fifth and sixth instar of F2 generation, endospores caused significant mortalities effect than other bacterial preparations, indicating that recombinant Bt strains can not only produce asporogenous strains of Bt but can also improve the toxicity of the crystal. Spores increased mortality and reducing the weight of surviving larvae by interacting with individual Bt toxins. The results indicated that cry + end plays a critical role in delaying the development of resistance to Bt products. Emberyo mortality percent due to cry + end reached to 45.0, 30.83 and 19.37 in F1, F2 and F3 generations respectively, although which due to endospores reached up to 40.83, 32.08 and 23.75 among three generations, respectively. This study assumed that the absence of spores in Bt toxin expressing transgenic plants and bacteria would accelerate evolution of pest resistance. Strategy of conjugation induced recombinant bioinsecticide used in this study was able to induce strains containing a unique combinations of cry genes conferring a wider activity spectrum than that of their parental strains.

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