Bt Cry proteins

Bee larval tests with Bt Cry proteins have been carried out in-house by biotech companies (S. Sims, personal communication), but there are no published reports of such work. Laboratory-based methods for rearing bee larvae have been established [48] and these could be adapted for use with Bt and other pest-resistance proteins, especially for the later larval instars which are known to ingest pollen as well as the glandular secretions of adult bees. 

Reduced binding of toxin is a primary mechanism of insect resistance to Cry proteins (Ferre and Van Rie, 2002). Resistance of the Indian meal moth to Bt was due to a 50-fold reduction in affinity of the membrane receptor (from brush borer membrane vesicles of larval midguts) for 5-endotoxin. In pinkbollworms, Bt resistance is associated with reduced binding of CrylAb to the brush borer membrane vesicle. Similarly, CrylAc resistance in diamondback moths was demonstrated to be due to dramatically reduced target binding. 

As mentioned, the 8-endotoxin (Cry protein) that makes up most of the conspicuous crystals is the main insecticidal component of B. thuringiensis. At sporulation, the majority of Bt strains produce crystalline inclusions that contain this insecticidal 8-endotoxin. The crystals account for 20% or more of the total bacterial protein at sporulation and may contain one or several endotoxins, which differ in activity. Many Bt toxin genes and genes for some... 

In view of the specificity of Cry proteins the effect of Bt crops on most nontarget insects can be expected to be minimal, especially when compared with the effects of broad-spectrum insecticides. In the case of Bt cotton and Bt com plants, both expressing lepidopteran-specific Cry proteins, some non-target Lepidoptera may be negatively affected when challenged with tissues of such Bt plants. Losey... 

The LOEC of pollen for all other events (Btll and MonSlO con9>rise the remaining 20% of total area planted a = 0.20) equals or exceeds 0.1% of expected pollen densities, dins die proportion of die monarch population at risk of inqiact from effects of Cry proteins, odier than event 176, in Bt cornfields in Iowa is ... 

The genes responsible for the crystal proteins are called cry genes, and the crystal toxin is called 5-endotoxin or Cry toxin, whereas the genes responsible for toxic cytosolic proteins (Cyt toxins) are called cyt genes. Many Bt strains are able to produce a number of such smaller cytosolic endotoxins in addition to the 8-endotoxins, but these are often deposited in inclusion bodies inside the crystals where they can comprise a considerable part of the crystal. Unlike the Cry toxins, the other toxins display a broader unspecific activity and may have some mammalian toxicity. They include the P-exotoxins, hemolysins, and enterotoxins. 

Bacillus thurigiensisx Naturally occurring bacterium present in soil, which produces a protein or toxin that interferes with the insect s digestion and acts as an insecticide. The genes that encode for this protein (cry) were introduced into maize to produce Bt maize. 

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