Insect Resistance Management

Crops with a Bacillus thuringiensis (Bt) trait have been modified to produce a protein that is toxic to various forms of insect larvae. Bt proteins are used as topical sprays in conventional and organic agriculture because they are effective and can be used safely. Crops that are genetically engineered to carry the Bt trait allow growers to protect their crops while eliminating or reducing the amount of pesticides sprayed.


The best way for growers to preserve the benefits and insect protection of Bt technology is to incorporate Integrated Pest Management (IPM) practices and to develop and implement Insect Resistance Management (IRM).  The IRM plan is used to decrease the possibility of an insect developing the ability to survive pesticide application or the ingestion of transgenic crops containing the Bt trait. Every grower of Bt corn products must comply with licensing terms and must have an IRM plan.


Integrated Pest Management Practices

Growers of Bt corn have found them to be highly compatible with their goals of IPM and sustainable agriculture.  Growers can enrich the sustainability of their corn agricultural systems by following suggested IPM practices, including cultural and biological control tactics, and proper use of pest thresholds and sampling.  These measures are not only important for non-Bt refuge acres, but are equally important for detecting and controlling non-target pests that exceed established thresholds on Bt crops.  Recommended IPM practices commonly adopted by growers of Bt crops include:


  1. Employing regular, appropriate scouting techniques and treatment decisions, especially during periods of heavy or sustained pest manifestation.
  2. Consulting a local crop advisor or extension specialist for the most up-to-date pest control information.
  3. Selecting insecticide actions that have minimal negative impact on beneficial insects, which are conserved by Bt-protected crops and contribute to insect pest control.
  4. Selecting cultivars well-adapted to their local ecology and giving appropriate attention to the impact of crop maturity and timing of harvest on pest severity.
  5. Using recommended cultural control methods to reduce pest overwintering, such as crop rotation and other soil management practices.


Insect Resistance Management Plans

The goal of an IRM plan is to decrease the probability of an insect developing the ability to survive a pesticide application, and a key component of any IRM plan is planting a refuge.  A refuge is simply a block or strip of the same crop that does not contain a Bt trait.  The lack of exposure to the Bt protein in refuges means that there will be vulnerable insects nearby to mate with any rare resistant insects that may emerge from the biotech crop.  To help reduce the risk of insects developing resistance, the refuge should be planted with a similar hybrid/variety, close to, and at the same time as, the crop containing Bt technologies.


Refuges are required by the Environmental Protection Agency (EPA) when planting Bt products. Here is the quick look at refuge/refuge requirements:


  1. Refuges can be planted in a variety of patterns, from strips within the field or in an adjacent field.
  2. Refuge requirements vary depending on the Bt crop being planted and region of the country.
  3. The percentage of refuge acres varies based on specific geography, but historically the required refuge for Bt corn has been 20 percent in Canada and the U.S. Corn Belt.
  4. Products that contain multi Bt traits present a lower risk of resistance and have lower refuge requirements.


In order to help ensure compliance, growers can try the new IRM Refuge Calculator. It's a tool designed for growers to help illustrate the appropriate refuge calculation, the quantity of standard seed bags to purchase for both trait and refuge and possible planting configurations for planting certain corn products in the United States.

Related Links

Insecticide Resistance Action Committee 
The Insecticide Resistance Action Committee (IRAC) was formed in 1984 and works as a specialist technical group providing a coordinated industry response to prevent or delay the development of resistance in insect and mite pests.




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