Bt-resistant Insects not Likely to Be a Problem for Maize Farmers – But CryF Resistance Re-emphasises the Need for Stacked Bt traits

The fall armyworm, Spodoptera frugiperda.
Photo by Clemson University –
USDA Cooperative Extension Slide Series, Bugwood.org.

-Cry1F resistance in fall armyworm Spodoptera frugiperda: single gene versus pyramided Bt maize — PLOS ONE

Abstract
Evolution of insect resistance to transgenic crops containing Bacillus thuringiensis (Bt) genes is a serious threat to the sustainability of this technology. However, field resistance related to the reduced efficacy of Bt maize has not been documented in any lepidopteran pest in the mainland U.S. after 18 years of intensive Bt maize planting.

Here we report compelling evidence of field resistance in the fall armyworm, Spodoptera frugiperda (J.E. Smith), to Cry1F maize (TC 3507) in the southeastern region of the U.S. An F2 screen showed a surprisingly high (0.293) Cry1F resistance allele frequency in a population collected in 2011 from non-Bt maize in south Florida. Field populations from non-Bt maize in 2012–2013 exhibited 18.8-fold to 85.4-fold resistance to purified Cry1F protein and those collected from unexpectedly damaged Bt maize plants at several locations in Florida and North Carolina had 85.4-fold resistance. In addition, reduced efficacy and control failure of Cry1F maize against natural populations of S. frugiperda were documented in field trials using Cry1F-based and pyramided Bt maize products in south Florida.

The Cry1F-resistant S. frugiperda also showed a low level of cross-resistance to Cry1A.105 and related maize products, but not to Cry2Ab2 or Vip3A. The occurrence of Cry1F resistance in the U.S. mainland populations of S. frugiperda likely represents migration of insects from Puerto Rico, indicating the great challenges faced in achieving effective resistance management for long-distance migratory pests like S. frugiperda.

...They’re probably from Puerto Rico (Entomology Today)

The North Carolina armyworms were indeed resistant to the Cry1F protein, which explained why they caused that North Carolina farmer so much trouble, since the corn variety that he was growing expressed the Cry1F protein only. This also led the researchers to believe that the armyworms probably originated from Puerto Rico.

“It’s a pretty solid assumption,” Dr. Reisig said. “Fall armyworms can’t overwinter in North Carolina because it’s too cold, and a previous study by Rodney Nagoshi and others showed that the North Carolina armyworms are genetically similar to those from Puerto Rico.”

@ Bt-resistant Insects not Likely to Be a Problem for Maize Farmers – Entomology Today:

Read more at:

- Discovery and Characterization of Field Resistance to Bt Maize:Spodoptera frugiperda (Lepidoptera: Noctuidae) in Puerto Rico

- Inferring the annual migration patterns of fall armyworm (Lepidoptera: Noctuidae) in the United States from mitochondrial haplotypes