Editing Genetically modified maize (section)

== Refuges ==
US [[Environmental Protection Agency]] (EPA) regulations require farmers who plant Bt corn to plant non-Bt corn nearby (called a refuge), with the logic that [[Maize#Pests|pests]] will infest the non-Bt corn and thus will not evolve a resistance to the Bt toxin.<ref name=Witowski>{{cite book | vauthors = Witkowski JF, Wedberg JL, Steffey KL, Sloderbeck PE, Siegfried BD, Rice ME, Pilcher CD, Onstad DW, Mason CE, Lewis LC, Landis DA, Keaster AK, Huang F, Higgins RA, Haas MJ, Gray ME, Giles KL, Foster JE, Davis PM, Calvin DD, Buschman LL, Bolin PC, Barry BD, Andow DA, Alstad DN | display-authors = 6 | veditors = Ostlie KR, Hutchison KR, Hellmich RL | chapter = How does resistance develop? | title = Bt Corn & European Corn Borer: Long-term Success Through Resistance Management | work = University of Minnesota Extension Office | publisher = North Central Region (NCR) | date = 1997 | url = http://www.extension.umn.edu/distribution/cropsystems/dc7055.html#ch11 | archive-url = https://web.archive.org/web/20130928064604/http://www.extension.umn.edu/distribution/cropsystems/dc7055.html#ch11 | archive-date=28 September 2013 }}</ref> Typically, 20% of corn in a grower's fields must be refuge; refuge must be at least 0.5 miles from Bt corn for [[lepidopteran]] pests, and refuge for [[corn rootworm]] must at least be adjacent to a Bt field.<ref name=Cullen>{{cite report |author=E. Cullen|author2=R. Proost, D. Volenberg|date=2008|title=Insect resistance management and refuge requirements for Bt corn|url=http://corn.agronomy.wisc.edu/Management/pdfs/A3857.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://corn.agronomy.wisc.edu/Management/pdfs/A3857.pdf |archive-date=2022-10-09 |url-status=live}}</ref> EPA regulations also require seed companies to train farmers how to maintain refuges, to collect data on the refuges and to report that data to the EPA.<ref name="Witowski" /> A study of these reports found that from 2003 to 2005 farmer compliance with keeping refuges was above 90%, but that by 2008 approximately 25% of Bt corn farmers did not keep refuges properly, raising concerns that resistance would develop.<ref name="Witowski" />

Unmodified crops received most of the economic benefits of Bt corn in the US in 1996–2007, because of the overall reduction of pest populations. This reduction came because females laid eggs on modified and unmodified strains alike, but pest organisms that develop on the modified strain are eliminated.<ref name="sci1009" />

Seed bags containing both Bt and refuge seed have been approved by the EPA in the United States. These seed mixtures were marketed as "Refuge in a Bag" (RIB) to increase farmer compliance with refuge requirements and reduce additional work needed at planting from having separate Bt and refuge seed bags on hand. The EPA approved a lower percentage of refuge seed in these seed mixtures ranging from 5 to 10%. This strategy is likely to reduce the likelihood of Bt-resistance occurring for [[corn rootworm]], but may increase the risk of resistance for [[lepidopteran]] pests, such as [[European corn borer]]. Increased concerns for resistance with seed mixtures include partially resistant larvae on a Bt plant being able to move to a susceptible plant to survive or cross pollination of refuge pollen on to Bt plants that can lower the amount of Bt expressed in kernels for ear feeding insects.<ref name="Siegfried">{{cite journal | vauthors = Siegfried BD, Hellmich RL | title = Understanding successful resistance management: the European corn borer and Bt corn in the United States | journal = GM Crops & Food | volume = 3 | issue = 3 | pages = 184–93 | year = 2012 | pmid = 22688691 | doi = 10.4161/gmcr.20715 | doi-access = free }}</ref><ref name="Devos">{{cite journal | vauthors = Devos Y, Meihls LN, Kiss J, Hibbard BE | title = Resistance evolution to the first generation of genetically modified Diabrotica-active Bt-maize events by western corn rootworm: management and monitoring considerations | journal = Transgenic Research | volume = 22 | issue = 2 | pages = 269–99 | date = April 2013 | pmid = 23011587 | doi = 10.1007/s11248-012-9657-4 | s2cid = 10821353 | url = https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2247&context=usdaarsfacpub }}</ref>