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Activities of modified Cry3A-type toxins on the red flour beetle, Tribolium castaneum (Herbst)

Authors

  • M. A. M. Mostafa,

    1. Biology Centre ASCR, Entomological Institute, České Budějovice, Czech Republic
    2. Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic
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  • J. Vlasák,

    1. Biology Centre ASCR, Entomological Institute, České Budějovice, Czech Republic
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  • F. Sehnal

    Corresponding author
    1. Biology Centre ASCR, Entomological Institute, České Budějovice, Czech Republic
    • Correspondence

      František Sehnal (corresponding author), Biology Centre ASCR, Entomological Institute, Branišovská 31, 370 05 České Budějovice, Czech Republic. E-mail: sehnal@bc.cas.cz

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Abstract

Bacillus thuringiensis (Bt) is a commonly used bioagent in insect pest control. Its toxicity is largely due to the crystalline (Cry) proteins that act selectively on insects and/or nematodes. Some insects, such as the stored product pest Tribolium castaneum, are relatively resistant to any natural Cry toxin. In attempt to find a Cry protein sufficiently toxic to this beetle, we prepared 18 recombinant modifications of Cry3A protoxins and tested them on the penultimate instar larvae of T. castaneum. Larvae were transferred to diet containing 0, 14, 28, 56 or 112 ppm of a Cry protein and their body growth and mortality were evaluated after 10 days. Cumulative mortality reached 25%, and the growth was nearly halted with 112 ppm of the natural Cry3Aa. The mortality was lower and the body weight increased by 15% of the control value in larvae receiving the recombinant Cry3Aa. Several structural derivatives of Cry3A also caused significant growth reduction and enhanced mortality. As both the natural and the recombinant Cry3Aa were more active than any of the tested Cry3A derivatives, we conclude that structural modifications of Cry3Aa are unlikely to increase toxicity to T. castaneum.

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