A study from northern China showed Bt cotton reduced pest populations in cotton and also other non-Bt crops growing nearby. Published in Science (Vol 321, No 5896), the study reported a dramatic reduction in cotton bollworms after the introduction of Bt cotton.
The researchers said Bt benefitted farmers by reducing the need for insecticide sprays.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/protecting-neighbours
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/down-earth
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/agriculture
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pest-control
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cotton
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/gm-crops
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-agricultural-research-institute-iari
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/china