Bt Cotton

Increased populations of beneficial insects

The use of broad spectrum insecticides, such as pyrethroids, on cotton has adversely affected and decreased the populations of non-target species including the arthropod natural enemies that can provide effective control of non-lepidopteran pests. Prior to the introduction of the Cry1Ac gene in Bt cotton in 1996, there was speculation that given the insecticidal specificity and effectiveness of the Bt proteins (English and Slatin 1992) used as topical sprays that arthropod natural enemies would be protected, increase in numbers, and have the potential to act as biological control agents and thus contribute to integrated pest management. Experimental studies confirmed that the arthropod natural enemy populations in Bt cotton are greater than in non-Bt cotton (Roof and DuRant 1997). In addition to reducing the number of sprays for the bollworm/budworm complex in the US, Bt cotton has also reduced the number of sprays for other insects such as thrips and aphids, by one or two sprays (Benedict and Altman 2001). This effect has been attributed to higher populations of beneficial predators and parasitic insects, that are depleted or eliminated by broad spectrum insecticide sprays.

There is evidence to indicate that significantly higher populations of economically important predatory bugs, spiders and ants are found in Bt cotton fields in comparison with fields treated with conventional insecticides (Head et al, In Press a). Beneficial insects appear to help control cotton pests in Bt cotton when the beneficial populations are not suppressed by insecticide sprays (Smith 1997). These data on beneficial populations all lend support to the thesis that Bt cotton can be effectively used as a building block for the foundation of an Integrated Pest Management strategy in cotton. There is increasing evidence from large scale studies of commercial Bt and conventional cotton in the southern US in 2000 that higher numbers of arthropod natural enemies are found in Bt cotton fields, compared with non-Bt cotton fields (Head et al, In Press a). The results confirm that Bt cotton provides a more favorable environment for species such as Geocovis, Orius, spiders and ants which act as biological control agents for control of secondary pests in Bt cotton fields. Similar effects have been reported in Bt cotton in China (Xia et al, 1999), where there was a significant reduction in number of broad spectrum insecticide sprays following the introduction of Bt cotton; insect predators increased by 24%.

Summary topics:

• Agronomic Benefits
• Environmental Benefits
  • Reduction in use of cotton insecticides
  • Less insecticides in aquifers and the environment
  • Farmer exposure to insecticide and health implications
  • Reduced production risks and enhanced opportunities to grow Bt cotton
  • Reduced risk for wildlife
  • Reduced fuel and raw material consumption, and pollution
• Social benefits
  • Social implications of saving water by reducing number of insecticide sprays
• Economic benefits
  • China
  • USA
  • India
  • Others
  • Distribution of economic surplus to Bt cotton stakeholders

Related topics:

• The cotton crop
• Global distribution of cotton in developing and industrial countries, by area, production, consumption, imports, and exports
• Number of cotton farmers worldwide and size of farms
• Insect pests of cotton
• Crop losses due to insect pests of cotton and the cost of control
• Global insecticide usage on cotton
• The use of Bt genes in cotton
• Assessment of environmental risk and Insect Resistance Management (IRM) strategies
• Global adoption of Bt cotton
• Bt cotton experience to date
• Summary: Agronomic, Environmental, Social and Economic Benefits
• Future global potential for Bt cotton: opportunities and challenges
• Highlights

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