Spin-off benefits of Bt insect resistance

GM crops are monitored post-release as part of studies to investigate the beneficial impact of GM traits like Bacillus thuringiensis (Bt) insect resistance, effects on non-target insects, and potential insect resistance.

American studies now show that, apart from economic benefits to Bt maize farmers, the reduction in stalk borer due to Bt also benefits farmers planting conventional maize. The studies covered five major states in the maize belt in the American Midwest, from introduction of Bt maize in 1996 to the 2009 marketing year and investigated impact on production of both Bt maize and non-Bt conventional maize. The Bt gene provides excellent resistance against the European maize borer Ostrinia. Many farms were inspected and occurance of larvae counted.

The cumulative benefits that accrued to both Bt and non-Bt maize farmers over the five states in terms of higher yields came to US,8 billion (R47 billion). Non-Bt maize production share amounted to about US,3 billion (R30 billion) or 63% of the total, as they didn’t need to buy more expensive seed, but gained from reduced borer infestation.
 
This finding was supported by larvae counts in adjacent fields of non-Bt maize that showed a reduction in numbers of between 27% and 73%, in direct relation to the share of areas planted to Bt cultures. The African stalk borers Busseola and Chilo are also controlled by Bt genes. Some South African maize farmers use Bt hybrids for early and late plantings but conventional hybrids for mid-spring planting, when borer risk is lower. [email protected]
Source: Tabashnik in Science, October 2010.   

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