Commercial History Of Plant Insecticidal Proteins

The use of transgenic plants modified to produce insecticidal proteins is a strategic departure from the remedial application of synthetic organic insecticides used in much of the twentieth century.1 In comparison to conventional insecticides, the substances contained within such plants are selectively toxic, more efficacious, and provide continuous protection from specific crop pests. The lepidopteran-active Cryl proteins derived from the common soil bacterium Bacillus thuringiensis Berliner (Bt) are the first commercially successful class of plant insecticidal proteins. Transgenic corn expressing Cryl proteins effective in controlling lepidopteran pests, especially European corn borer (Ostrinia nubilalis Hübner, ECB), were first available to U.S. growers in 1996. Widespread adoption of this technology has occurred, with 40% of corn hectares in the United States planted to Bt varieties.2 Even wider adoption of the Bt technology has occurred for cotton in the United States where 57% of cotton hectares are planted to lepidopteran-active Bt varieties.2 Globally, nearly 26.3 million hectares of Bt crops were planted in 2005.3 Early successful entries into the commercial market were corn expressing CrylAb, cotton expressing CrylAc, and, more recently, corn expressing CrylF. In addition to these commercially successful products, certain early market Bt entries failed due to performance or management concerns (Bt corn expressing either CrylAb [Event l76], CrylAc, or Cry9C; Bt potato expressing Cry3A).

Continuing innovation has led to the recent and pending commercialization of other plant-expressed insecticidal proteins, including Cry3Bb and Cry34Abl/ Cry35Abl for controlling western corn rootworm (Diabrotica virgifera virgifera LeConte, CRW) and Cry2Ab for improving efficacy against several lepidopteran pests in cotton. Stacked protein products are now available where the transgenic crop expresses dual Bt toxins with each toxin intended for control of different target species. An example is YieldGard® Plus corn that expresses CrylAb and Cry3Bb proteins for control of ECB and CRW, respectively. Additionally, pyramided proteins with similar but complementary activity are being used to improve both activity spectrum and resistance management. For instance, Bollgard® II cotton combines CrylAc and Cry2Ab proteins in a pyramid to broaden efficacy and spectrum of control of lepidopteran pests. Vegetative insecticidal proteins (VIPs) derived from Bt represent another class of proteins active against lepidopteran pests.4-6 Vip3A is currently being developed for insect control in cotton in the United States. Discovery of novel insecticidal proteins from Photorhabdus luminescens7,8 and their expression in plants,9 as well as Cry5 proteins effective against nematodes,l0 show promise for further development of pest-protected transgenic crops using bacterial proteins.

In light of the fact that plant-expressed insecticidal proteins are widely deployed in the environment, their ecological safety is an important consideration. Recent reviews offer perspectives on the effects of insecticidal proteins on nontarget organ-isms.11-13 The following sections describe the body of data on plant-expressed insec-ticidal proteins as it relates to ecological risk assessment and regulation.

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