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Bt - Moving to a Second GenerationThe early promise of insect resistance (IR) traits in genetically modified (GM) crops has been confirmed by their widespread adoption in the USA and the reduced use of conventional insecticides. The “second generation” IR traits now becoming available will reduce insecticide use further, with some associated benefits for the environment, as CPM’s North American correspondent, Duncan Allison, reports. US developments with Bt maizeConvenience and ease of management have been underrated in understanding the adoption of biotech traits by farmers, particularly for control of weeds but also for insects. It has always been difficult to time foliar applications for optimal control of corn borers (Ostrinia nubilalis). Use of Bt maize does not require careful monitoring and spraying and provides control that also translates into reduced aflatoxin levels in the grain. US farmers used Bt maize on 29% of the planted acres in 2003, many more than were ever sprayed in the past with insecticide. After its first year of commercialisation, Dow’s Herculex 1, which contains the Bt Cry1F gene, has been able to add the western bean cutworm (Loxagrotis albicosta) to the list of insects controlled on the label. Interest has been strong in regions with black cutworm (Agrotis ipsilon) due to the control that Herculex 1 provides. The big news in 2003 was undoubtedly Monsanto’s launch of YieldGard Rootworm providing control of the “billion dollar insect”, Diabrotica spp (CPM February & November 2003). US farmers used YieldGard Rootworm varieties on just under one million acres (over 400,000 hectares) in 2003. Interest will be high in 2004 in YieldGard Plus, which was registered in November 2003 and provides control of both corn borer and rootworm (CPM April 2002 & February 2003). Most seed companies are offering seed treatments with the recently registered Poncho (clothianidin) or Cruiser (thiamethoxam), so that farmers will not need to use conventional soil or foliar insecticides for control of soil insects. Bt cotton in the USASome 41% of planted acres of US cotton in 2003 were planted with Bt varieties and this area will grow further in 2004 with the introduction of second generation IR traits in cotton. Amongst these are Monsanto’s Bollgard II, which contains the two Bt genes, Cry1Ac and Cry2Ab. This provides control of tobacco budworm (Heliothis virescens) and cotton bollworm (Helicoverpa zea), as well as the other major lepidopterous insects. Dow’s WideStrike contains two Bt genes, Cry1F and Cry1Ac; Syngenta’s VipCot cotton contains exotoxin proteins rather than the conventional Bt endotoxins. These products will introduce some real competition to the cotton biotech IR trait market that has been dominated so far by Monsanto. Both WideStrike and VipCot are expected to be registered in time for the 2004 season and available in cotton varieties to provide control of the major lepidopterous insects. The EPA gained sufficient confidence in 2001 to renew the initial five-year Bt registration to the end of 2006 for cotton and the end of 2008 for maize. This was the culmination of a very thorough process of reassessing the health and safety of Bt to non-target organisms, demonstration of lack of accumulation in the soil as well as other factors. Bt traits and resistance concernsThere has been major concern about targeted insects developing resistance to the Bt genes in maize and cotton. A condition of registration has been for growers to ensure that untreated Bt-free “refugia” represented 20% of the area planted with Bt traits. There has been discussion about how closely this insect resistance management (IRM) programme has been followed but the fact is that widespread monitoring has failed to find any resistant insect biotypes in the field. An article in the September 2003 edition of Nature Biotechnology has confirmed US experience and indicated that insect resistance to Bt has also not been found in China and Australia after at least five years of use. There is now debate as to whether such stringent IRM requirements are necessary. New insect-resistant genesRecent developments are also encouraging in relation to the development of combinations of Bt genes, new proteins and genes with completely new and different mode of action. The second-generation traits in cotton have two genes with little homology in Bollgard II and Syngenta’s VipCot has a protein with novel mode of action. Research in both the USA and Europe indicates that Photorhabdus bacteria may provide genes producing proteins with totally different modes of action and control of an even broader spectrum of insects. IR traits are confirming their promise by reducing conventional insecticide use without any concomitant insect resistance developing. Biopesticides - the Future?Horticulture Research International (HRI) held a conference at its headquarters in Wellesbourne, Warwickshire, UK (www2.hri.ac.uk), on 18 November 2003 to consider the future of biopesticides in sustainable crop protection. The event focused on why effective products are not reaching UK growers, as Martin Redbond reports. Biopesticides slow to reach UK growersDr David Chandler (HRI) said that interest in alternative pest control methods has grown in response to consumer concerns about the safety of pesticide residues in food and the environmental impact of broad-spectrum chemical pesticides. Other factors include the withdrawal of products following UK and EU reviews and the development of resistance. Unfortunately, he commented, commercial biopesticides are slow to reach UK growers. Dr Chandler estimated that over 100 bio-insecticides were available globally but only a handful in the UK. He attributed this to the current regulatory systems that encourage biopesticides to be developed, commercialised and used according to an inappropriate “chemical pesticide model”. Dr Chandler’s colleague, Professor John Whipps, said that public concern and the withdrawal of many active ingredients was also driving interest in the development and use of biological methods of control for plant diseases. Work in this area at HRI is focused on understanding different methods of control. These range from the use of microbial inoculants or biopesticides as replacements for chemicals to the development of disease suppressive systems for plant growth. He said that nearly 80 products which exhibit some disease biocontrol activity are sold worldwide but only one is currently registered in the UK. |