Bt crops

Bt crops
Name	Bt crops
Use	Insect resistance
Developer	Monsanto, Syngenta, Dow AgroSciences
First use	1996
Related	Genetic engineering, Transgenic plants

Bt crops. They are a class of transgenic plants genetically modified to express insecticidal proteins derived from the soil bacterium Bacillus thuringiensis. First commercialized in the mid-1990s, these crops provide inherent protection against specific orders of Lepidoptera, Coleoptera, and Diptera, reducing the need for broad-spectrum chemical insecticide applications. Their adoption has been widespread, particularly in major agricultural nations, leading to significant shifts in pest management strategies and ongoing debates within agricultural science.

History and development

The foundational discovery of the insecticidal properties of Bacillus thuringiensis dates to the early 20th century, with its initial use as a microbial spray in France. The pivotal breakthrough for modern Bt crops occurred in the 1980s when scientists at Agracetus and Monsanto successfully isolated the cry gene responsible for toxin production. This research was accelerated by collaborations with institutions like Cornell University and the University of California, Berkeley. The first commercial approval was granted by the United States Environmental Protection Agency in 1995 for Bt potato, followed rapidly by the launch of Bt cotton and Bt maize in 1996 by Monsanto and Ciba-Geigy.

Mechanism of action

The insecticidal activity is mediated by Cry proteins and Cyt proteins produced by genes from Bacillus thuringiensis. These proteins are protoxins that are activated upon ingestion by susceptible insect larvae in the alkaline environment of the midgut. The activated toxins bind to specific cadherin receptors on the gut epithelium, such as those found in Helicoverpa zea, creating pores that cause cell lysis, septicemia, and eventual larval death. This mode of action is highly specific, largely nontoxic to mammals, birds, and most beneficial insects including Apis mellifera.

Types and applications

Primary commercial Bt crops include Bt cotton, engineered to combat the cotton bollworm and pink bollworm, and Bt maize, which targets the European corn borer and corn rootworm. Other significant varieties are Bt soybean and Bt eggplant, the latter notably adopted in Bangladesh. These crops are often deployed as part of integrated pest management systems and are frequently stacked with traits for glyphosate tolerance, a technology pioneered by companies like Dow AgroSciences and Pioneer Hi-Bred.

Environmental impact

Studies, including those by the United States Department of Agriculture, have documented a reduction in the volume of synthetic insecticides applied, particularly on crops like Bt cotton in China and India. This reduction can benefit populations of non-target organisms such as Lepidoptera butterflies and natural enemies like Coccinellidae. However, concerns persist regarding effects on soil ecosystems, potential gene flow to wild relatives, and impacts on monarch butterfly populations, a subject of research at the University of Minnesota.

Economic and social effects

The adoption of Bt crops has led to documented yield increases and lower production costs for many farmers, as reported by the International Food Policy Research Institute. In regions like Maharashtra, this has translated into improved incomes for smallholders. Conversely, issues such as increased seed cost, technology use agreements with firms like Monsanto, and farmer debt have sparked social movements, including the Shetkari Sanghatana in India. The global market is dominated by Corteva Agriscience and Bayer.

Resistance management

The evolution of insect resistance is a major threat, documented in species like Busseola fusca in South Africa. To delay resistance, strategies like the high-dose/refuge strategy are mandated by the Environmental Protection Agency. This requires planting structured refuges of non-Bt crops to maintain populations of susceptible insects. Monitoring programs, such as those coordinated by the Arizona Cooperative Extension, track resistance alleles in pests like the pink bollworm.

Regulation and controversy

Bt crops are stringently regulated by bodies including the Food and Drug Administration, the European Food Safety Authority, and the Cartagena Protocol on Biosafety. Controversies are multifaceted, involving disputes over intellectual property led by organizations like the Erosion, Technology and Concentration Group, concerns about biodiversity from Greenpeace, and international trade disputes adjudicated by the World Trade Organization. The debate often centers on the precautionary principle and labeling initiatives such as Proposition 37 in California.

Category:Agricultural technology Category:Genetic engineering Category:Biotechnology