<P> In 1996 another class of insecticidal proteins in Bt was discovered; the vegetative insecticidal proteins (Vip). Vip proteins do not share sequence homology with Cry proteins, in general do not compete for the same receptors, and some kill different insects than do Cry proteins . </P> <P> In 2000, a novel functional group of Cry protein, designated parasporin, was discovered from noninsecticidal B. thuringiensis isolates . The proteins of parasporin group are defined as B. thuringiensis and related bacterial parasporal proteins that are not hemolytic, but capable of preferentially killing cancer cells . As of January 2013, parasporins comprise six subfamilies: PS1 to PS6 . </P> <P> Spores and crystalline insecticidal proteins produced by B. thuringiensis have been used to control insect pests since the 1920s and are often applied as liquid sprays . They are now used as specific insecticides under trade names such as DiPel and Thuricide . Because of their specificity, these pesticides are regarded as environmentally friendly, with little or no effect on humans, wildlife, pollinators, and most other beneficial insects, and are used in organic farming; however, the manuals for these products do contain many environmental and human health warnings, and a 2012 European regulatory peer review of five approved strains found, while data exist to support some claims of low toxicity to humans and the environment, the data are insufficient to justify many of these claims . </P> <P> New strains of Bt are developed and introduced over time as insects develop resistance to Bt, or the desire occurs to force mutations to modify organism characteristics or to use homologous recombinant genetic engineering to improve crystal size and increase pesticidal activity or broaden the host range of Bt and obtain more effective formulations . Each new strain is given a unique number and registered with the U.S. EPA and allowances may be given for genetic modification depending on "its parental strains, the proposed pesticide use pattern, and the manner and extent to which the organism has been genetically modified". Formulations of Bt that are approved for organic farming in the US are listed at the website of the Organic Materials Review Institute (OMRI) and several university extension websites offer advice on how to use Bt spore or protein preparations in organic farming . </P>

Where did the genetically modified bt in crops originally come from and what does it do