Researchers from the University of Arizona Department of Entomology in the
College of Agriculture, Life and Environmental Sciences used genomics to
investigate the genetic changes causing resistance to transgenic crops in
field populations of the corn earworm, also known as cotton bollworm or
Helicoverpa zea.



The researchers, led by Bruce Tabashnik, head of the Department of
Entomology, discovered that in this pest, field-evolved resistance was not
associated with any of the 20 genes that have been previously implicated in
resistance to the pest-killing proteins in transgenic crops. The U of A
researchers worked with colleagues from Texas A&M University who used
bioassays to evaluate resistance by testing the insects from the field. The
collaborating research teams analyzed 937 corn earworms from 17 sites in
seven states across the southern United States, sampled from 2002 to 2020.



"We carefully examined 20 genes that affected how pests responded to Bt
proteins in previous studies. Our evidence indicates changes in these genes
are not causing resistance to Bt crops in wild populations of the corn
earworm," said Andrew Legan, a U of A postdoctoral fellow and first author
of the study. Legan added that they found resistance was associated with a
cluster of genes that was duplicated in some resistant field populations.
However, it remains a mystery as to how many of these genes contribute to
resistance and how they confer resistance.



Despite not narrowing the cause of resistance to a single gene, researchers
say their study provides an important reminder that the genetic basis of
resistance can differ between the field and lab.



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