Bacillus thuringiensis is a spore-forming bacterium species that is commonly found in soil. Bt contains a native crystal protein that when ingested by insect pests, causes paralysis in the digestive tract that is lethal. Bt foliar sprays have been used for 50 years to control insect pests and have a long history of safe use. Bt sprays are one of few insecticides permitted for use in organic farming. The commercial Bt cotton available today contains genes from the isolate B. thuringiensis, ssp kurstaki that produces Cry1Aa, Cry1Ab, Cry1Ac, Cry2A (Benedict and Altman 2001).

A. Bollgard® and the Chinese Bt Fusion Gene

The Bt genes that are currently deployed are from two sources. Monsanto developed and deployed the Cry1Ac gene in its Bollgard® varieties, which are the most widely used in all nine countries that grow Bt cotton. The second source is the Bt fused gene that was developed by the public sector Chinese Academy of Agricultural Sciences (CAAS) in Beijing, China. The commercial plantings of the CAAS Bt cottons feature a modified Bt fusion gene, Cry1Ab/Cry1Ac, planted in the four provinces of Anhui, Shangdong, Shanxi, and Hubei. (Jia 1998, James 1998). The cowpea trypsin gene, CpTi with a different mechanism of insect resistance to Bt, has also been incorporated by CAAS as a stacked gene with Bt in some varieties. By 1999, the CAAS single gene Bt cottons, and the stacked Bt/CpTi cottons, designed to provide more durable resistance, were planted in nine provinces compared with four in 1998.

The most prevalent Bt gene on a global basis, Cry1Ac, was incorporated into Coker 312 cotton designated MON 531 by Monsanto (Perlak et al 2001) and later named Bollgard^® cotton; high transformation efficiency was achieved in Coker with Agrobacterium tumefaciens. The transformed Coker was then backcrossed with lines fom Delta and Pine Land and other companies that had the necessary agronomic qualities for commercial acceptance. The data in Table 13 demonstrate the efficacy of the Cry1Ac in Bollgard^® in controlling the major lepidopteran pests of cotton. The highest level of control is achieved for pink bollworm (99%) followed by tobacco budworm (95%) and bollworm at 70 to 90%. Control of other cotton pests, cotton leaf perforator and saltmarsh caterpillar is at 85% or more, whereas fall armyworm is at 20%.

The advantages of the Cry1Ac in Bollgard^®, over the Bt cotton spray, summarized by Benedict and Altman, (2001), are as follows:

Coincidental with the deployment of the current Bt genes in commercial cotton, R&D programs were developing improved Bt cottons. The first of these to be approved for commercial production was the dual Bt gene Bollgard^® II from Monsanto which was approved in September 2002 for planting in Australia for the 2002/03 season with plans to release it commercially in the US once regulatory approval is granted (expected in 2003). Dow AgroSciences have also announced that they expect to launch a dual gene Bt cotton in the US in 2004 (Dow AgroSciences 2002) and Syngenta plans to release a cotton with a novel VIP insect-resistance gene in the US in 2004 with a further release in Australia (Syngenta 2002).

B. Bollgard^® II Cotton

Bollgard^®, the first generation Bt cotton developed by Monsanto, with one Bt gene Cry1Ac, has been successfully grown on over 10 million hectares by millions of farmers in nine countries since its introduction in 1996. Producers have benefited from reduced insecticide usage, higher yields and higher economic returns, whereas society has benefited from a safer environment and more affordable cotton prices. Bollgard^® has delivered substantial agronomic, environmental health and economic benefits to both small and large farmers in developing and industrial countries.

The Insect Resistance Management (IRM) Strategy for Bt cotton that Monsanto, in conjunction with USDA and universities, developed prior to the introduction of Bollgard® had anticipated further developments of Bt cotton and planned for the development of a second generation of an improved Bt cotton with two Bt genes, now designated Bollgard^® II. The new product, Bollgard^® II, Event 15985 was developed using particle acceleration plant transformation procedures to add the Cry2Ab gene to the cotton line DP50B that already had the Cry1Ac (Carpenter et al 2002, Rahn et al 2001). The Bollgard^® II second-generation of Bt cotton technology contains two different genes that encode proteins from Bacillus thuringiensis: Cry2Ab and Cry1Ac; the latter is the protein in the first generation of Bt cotton products. The dual gene cultivars are expected to provide growers with a broader control over a wider variety of insects than achieved with the first generation Bt cotton products while maintaining the excellent control of tobacco budworm (Heliothis virescens (F.)) and pink bollworm (Pectinophora gossypiella (Saunders)) (Perlak et al 2001). Improved efficacy against several insect pests has been demonstrated in laboratory assays and under field conditions. Laboratory bioassays (Perlak et al 2001) using isolated plant tissue have shown that the dual Bt gene cultivars have increased activity (Table 14) against cotton bollworm (Helicoverpa zea (Boddie), control is increased from 84.4 to 92.2%), fall armyworms (Spodoptera frugiperda (J.E. Smith), 16.1 to 100%), beet armyworms (Spodoptera exigua (Hubner) 50.1 to 94.9%) and soybean looper (1.2 to 97.4% Perlak et al 2001, Stewart et al 2001). Bollworm survival specifically on flower structures was also shown to be significantly lower with the dual Bt gene plants in fresh tissue bioassays (Gore et al 2001). In field studies, cotton genotypes expressing both genes sustained significantly less terminal, square and boll damage from cotton bollworms compared to single gene Bt cotton, albeit under low levels of bollworm pressure (Jackson et al 2001, 2000). Improved field efficacy was also observed for pink bollworm in studies in Arizona, USA (Marchosky et al 2001).

In addition to enhancing efficacy, the dual Bt gene product can, most importantly, serve as a new tool to combat the potential development of insect resistance in cotton fields by providing a second mode of action to control these pests. The Cry2A proteins have characteristics distinct from the Cry1Ac protein (English and Slatin 1992, English et al 1994) and the amino acid sequences of the proteins are quite dissimilar with less than 30% sequence identity (Crickmore et al 1998). Paired genes are one tool used to delay the onset of resistance (Roush 1994, Gould 1998). The evidence indicates that Cry2Ab does provide a second, independent high dose against tobacco budworm and thus the paired toxins may result in redundant control, aiding resistance management strategies (Greenplate et al, In press).

Thus, Bollgard^® II represents an important development from three perspectives. First, the two genes reduce the probability of resistance developing and this is a very important contribution to the durability of Bt resistance (Gould 1998); second, it increases the efficacy of control for some of the major lepidopteran pests ,and third it increases the spectrum of pests that can be controlled to include several secondary pests, including armyworms and loopers. Extensive field trials confirm that Bollgard^® II provides improved control (Catchot 2001, Norman and Sparks 2001, Lorenz et al 2001, Penn et al 2001, Ridge et al 2000). Gianessi et al (2002) estimated that planting Bollgard^® in the US alone in 2001 reduced insecticide applications by 848 MT. Enhanced control with Bollgard^® II of the principal cotton bollworm/budworm complex and control of secondary lepidopteran pests should further reduce insecticide requirements in the US and increase yield and collectively facilitate the implementation of IPM and contribute to a more sustainable and profitable cotton production system.

Bollgard^® II was approved for use in Australia in September 2002, and it is expected that up to 5,000 hectares will be planted in 2002/03, with a plan for it to replace the single gene construct, INGARD^®, entirely in 2004/05. Unlike the single construct, which was limited to 30% of the area, Bollgard^® II is not subject to the 30% restriction, and eventually will probably occupy 70% or more of the cotton area in Australia. Approval of Bollgard^® II is pending in the US and is expected to be cleared imminently for introduction in the US in 2003. It is likely that Bollgard^® I will be phased out of commercial production in the US after Bollgard^® II becomes available. Bollgard^® II is an important new element in the insect resistant management strategy of cotton insect pests; it provides an additional important tool for facilitating the implementation of IPM, and for optimizing the durability of Bt genes and the multiple and significant benefits they offer.

C. Other Expected New Insect Resistant Cottons

In 2002, Dow AgroSciences announced the development of a new Bt cotton with traits that confer broad spectrum resistance to lepidopteran pests of cotton; these include tobacco budworm, bollworm, pink bollworm, beet and fall armyworms and loopers. The new Bt cotton product contains the dual genes Cry1Ac and Cry1F, transformed with Agrobacterium tumefasciens, and incorporated through back-crossing into several high quality commercial varieties of cotton. (Dow AgroSciences 2002, Personal Communication).

An experimental use permit was filed with the EPA in late 2001 and a complete regulatory package will be submitted following the 2002 season, with full U.S. approval anticipated in early 2004. The new Bt cotton will be marketed through Phytogen Seed Co., and Dow AgroSciences is discussing broad licensing of the product with several other cotton seed companies in the US; opportunities for international marketing of the product are being explored. Import approval for the product is being pursued in Japan, Canada and Mexico.

Syngenta plans to release a cotton with a novel VIP insect resistance gene in the US in 2004 with a further release in Australia (Syngenta 2002).