A website from UGA Cooperative Extension


This morning I found an interesting article on Ag Fax.com about B.t. resistant fall armyworms. Doug Johnson of the University of Kentucky wrote the article to address the state’s potential risk to the resistant population. The interest started with the discovery of a resistant population in North Carolina in field corn. Scientists from NCSU discovered this population carries a gene that makes it resistant to the B.t. trait Cry1F.

This trait generally confers protection from caterpillar feeding in cotton (Widestrike) and corn (Herculex 1). This resistance has never before been reported further north than Louisiana or Florida.

Dr. Dominic Reisig found FAW feeding and surviving on Cry1F, B.t. corn in North Carolina.

Fall armyworms can only survive the winter where its food plants grow all year round. Which means FAW cannot survive northern winters. Moths migrate northward each spring from two very different sources: southern Florida and southern Texas.

FAW migration

The Florida population contains individuals with resistance to the Cry1F trait. The Texas population does not have this modified gene. Why only Florida? This is likely because the Florida population interbreeds with populations in the Caribbean which are the probable source of the resistance. South Florida and the Caribbean have year-round FAW populations and lots of use and testing of single trait corn products. It appears that the Texas population does not mix with the Florida population very much so it has not acquired the resistance gene.

“This is a huge wake-up call for farmers north of Louisiana and Florida – this is definitely something to keep an eye on,” Reisig says. “Resistance happens, and it’s a stark reminder that we need to take steps – such as planting non-Bt ‘refuge’ crops near the Bt crops – to limit the development of resistant insect strains.”

The real fear is that these Bt-resistant armyworms will move from corn to cotton.

“That would be problematic, since cotton usually begins producing fruit (the marketable cotton bolls) in July or early August – when fall armyworm populations have grown,” Reisig says. “Corn is less threatened, since it is at its most vulnerable in the spring, when fall armyworm populations are still low.

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