Abstract
Abstract A 6-yr field study assessed the long-term impact of Bt cotton producing the Cry1Ac δ-endotoxin on 22 taxa of foliar-dwelling arthropod natural enemies in Arizona. No chronic, long-term effects of Bt cotton were observed over multiple generations of nontarget taxa. Zero-2 taxa declined significantly in unsprayed Bt compared with non-Bt cotton each year. In contrast, positive control studies showed that insecticide applications for caterpillars and other pests in both non-Bt and Bt cotton had much greater negative effects on 10 taxa. Multivariate principal response curves supported the findings of univariate analyses for the entire natural enemy community, showing no effect of Bt cotton but large and long-lasting negative effects from the use of insecticides. Multi-year analyses provided greater statistical power and indicated significant reductions that averaged 19% in five arthropod predator taxa in unsprayed Bt compared with non-Bt cotton. Most of these reductions were likely associated with reductions in lepidopteran prey. However, results of a companion study examining natural enemy function suggest that these minor reductions in Bt cotton have little ecological meaning. Multi-year analyses showed an average significant reduction of 48% in 13 taxa for plots receiving insecticide applications. On average, a 3-yr study with four replicates per year was sufficient to discern changes of ≈20%, with 80% power in unsprayed cotton. This long-term study indicates that the effects of Bt cotton on a representative nontarget community are minor, especially in comparison with the alternative use of broad-spectrum insecticides. Guidelines for improving nontarget field studies are discussed.
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Claims 10
Claim · model-written summary
Bt cotton showed no chronic long-term effect on nontarget natural enemy taxa over multiple generations.
Verbatim
e0“No chronic, long-term effects of Bt cotton were observed over multiple generations of nontarget taxa.”
e1“Zero-2 taxa declined significantly in unsprayed Bt compared with non-Bt cotton each year.”
Claim · model-written summary
Between zero and two natural enemy taxa declined significantly each year in unsprayed Bt cotton compared with non-Bt cotton.
Verbatim
e0“Zero-2 taxa declined significantly in unsprayed Bt compared with non-Bt cotton each year.”
t0“Bt Cotton”
Claim · model-written summary
Insecticide applications for caterpillars and other pests caused substantially greater negative effects on 10 natural enemy taxa in both Bt and non-Bt cotton.
Verbatim
e0“insecticide applications for caterpillars and other pests in both non-Bt and Bt cotton had much greater negative effects on 10 taxa.”
t0“Bt Cotton”
Claim · model-written summary
Principal response curve analysis showed no effect of Bt cotton on the natural enemy community.
Verbatim
e0“Multivariate principal response curves supported the findings of univariate analyses for the entire natural enemy community, showing no effect of Bt cotton but large and long-lasting negative effects from the use of insecticides.”
e1“Zero-2 taxa declined significantly in unsprayed Bt compared with non-Bt cotton each year.”
Claim · model-written summary
Principal response curve analysis showed large and long-lasting negative insecticide effects on the natural enemy community.
Verbatim
e0“Multivariate principal response curves supported the findings of univariate analyses for the entire natural enemy community, showing no effect of Bt cotton but large and long-lasting negative effects from the use of insecticides.”
e1“positive control studies showed that insecticide applications”
Claim · model-written summary
Across years, five arthropod predator taxa averaged a significant 19% reduction in unsprayed Bt cotton relative to non-Bt cotton.
Verbatim
e0“Multi-year analyses provided greater statistical power and indicated significant reductions that averaged 19% in five arthropod predator taxa in unsprayed Bt compared with non-Bt cotton.”
Claim · model-written summary
The authors attributed most predator reductions in Bt cotton to reduced lepidopteran prey.
Verbatim
e0“Most of these reductions were likely associated with reductions in lepidopteran prey.”
e1“Multi-year analyses provided greater statistical power and indicated significant reductions that averaged 19% in five arthropod predator taxa in unsprayed Bt compared with non-Bt cotton.”
Claim · model-written summary
A companion study suggested that minor natural enemy reductions in Bt cotton have little ecological meaning.
Verbatim
e0“results of a companion study examining natural enemy function suggest that these minor reductions in Bt cotton have little ecological meaning.”
Claim · model-written summary
Multi-year analyses showed an average significant 48% reduction in 13 natural enemy taxa in insecticide-treated plots.
Not reportedComparator
Verbatim
e0“Multi-year analyses showed an average significant reduction of 48% in 13 taxa for plots receiving insecticide applications.”
e1“in both non-Bt and Bt cotton”
Claim · model-written summary
A three-year unsprayed cotton study with four replicates yearly was sufficient on average to detect changes of about 20% with 80% power.
- Taxon
- cotton
Gossypium hirsutume0 - Outcome
- powere0
- Value
- 80%e0
- Qualifier
- a 3-yr study with four replicates per yeare0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“On average, a 3-yr study with four replicates per year was sufficient to discern changes of ≈20%, with 80% power in unsprayed cotton.”
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See all 7 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.