Skip to Main Content
U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Home > Search > Publication Information

  1. Share via EmailShare on FacebookShare on LinkedInShare on Twitter
    Dislike this pubLike this pub
    Author(s): Leah S. Bauer
    Date: 1995
    Source: Florida Entolomogist. 78(3): 414-443.
    Publication Series: Scientific Journal (JRNL)
    Station: North Central Research Station
    PDF: View PDF  (383.98 KB)

    Description

    Insecticidal crystal proteins (also known as d-endotoxins) synthesized by the bacterium Bacillus thuringiensis Berliner (Bt) are the active ingredient of various environmentally friendly insecticides that are 1) highly compatible with natural enemies and other nontarget organisms due to narrow host specificity, 2) harmless to vertebrates, 3) biodegradable in the environment, and 4) highly amenable to genetic engineering. The use of transgenic plants expressing Bt d-endotoxins has the potential to greatly reduce the environmental and health costs associated with the use of conventional insecticides. The complex mode of action of Bt is the subject of intensive research. When eaten by a susceptible insect d-endotoxin crystals are solubilized in the midgut; proteases then cleave protoxin molecules into activated toxin which binds to receptors on the midgut brush border membrane. Part of the toxin molecule inserts into the membrane causing the midgut cells to leak, swell, and lyse; death results from bacterial septicemia. Insecticides formulated with Bt account for less than 1% of the total insecticides used each year worldwide because of high cost, narrow host range, and comparatively low efficacy. Environmental contamination, food safety concerns, and pest resistance to conventional insecticides have caused a steady increase in demand for Bt-based insecticides. The recent escalation of commercial interest in Bt has resulted in more persistent and efficacious formulations. For example, improved Bt-based insecticides have allowed management of the diamondback moth, Plutella xylostella (L.). Unfortunately this has resulted in the evolution of resistance to?na-endotoxins in P. xylostella populations worldwide. The recent appearance of Bt resistance in the field, corroborated by the results of laboratory selection experiments, demonstrates genetically-based resistance in several species of Lepidoptera, Diptera, and Coleoptera. The genetic capacity to evolve resistance to these toxins is probably present in all insects, and the heritability, fitness costs, and stability of the resistance trait are documented in several insect populations. In two strains of Bt-resistant lepidopteran species, mechanisms of resistance involve reductions in the binding of toxin to midgut receptors. Research on other resistant strains suggests that other mechanisms are also involved. Unfortunately, the high stability of the resistance trait, as well as broad spectrum cross-resistance to other d-endotoxins, undermines many potential options for resistance management. Genetically engineered plants, expressing d-endotoxin continuously and at ultrahigh doses, ensure intense and rapid selection?nof the target insect population. The efficacy of transgenic plants can be preserved only by developing an integrated pest management program that is designed specifically to reduce selection pressure by minimizing exposure to Bt and increasing other mortality factors, thereby slowing the rate of pest adaptation to Bt.

    Publication Notes

    • Check the Northern Research Station web site to request a printed copy of this publication.
    • Our on-line publications are scanned and captured using Adobe Acrobat.
    • During the capture process some typographical errors may occur.
    • Please contact Sharon Hobrla, shobrla@fs.fed.us if you notice any errors which make this publication unusable.
    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Bauer, Leah S. 1995. Resistance: a threat to the insecticidal crystal proteins of Bacillus thuringiensis. Florida Entolomogist. 78(3): 414-443.

    Keywords

    d-endotoxin, cross-resistance, transgenic plants, resistance management-endotoxin, cross-resistance, transgenic plants, resistance management

    Related Search


    XML: View XML
Show More
Show Fewer
Jump to Top of Page