The fall armyworm (Spodoptera frugiperda) is an important pest of maize in
the United States and many tropical areas in the western hemisphere.
Herculex I maize with the Cry1F gene was planted to control Lepidopteran
pests, including S. frugiperda. A population of fall armyworm (Spodoptera
frugiperda) discovered in Puerto Rico in 2006 had evolved resistance to
Cry1F maize in the field, the first documented case of an insect with field
resistance to a Bt plant. This resistant population was utilized in
tri-trophic studies conducted with Cotesia marginiventris, a larval
endoparisitoid of the fall armyworm.

The Cry1F-resistant S. frugiperda were studied to evaluate effects of Cry1F
on Cotesia marginiventris over five generations. Possible prey-mediated
effects were overcome and concerns about potential differences in laboratory
or field-derived Bt resistance were avoided. Results clearly demonstrate
that Cry1F maize does not affect development, parasitism, survivorship, sex
ratio, longevity or fecundity of C. marginiventris when they parasitize
Cry1F maize-fed S. frugiperda. Moreover, the level of Cry1F protein in the
leaves was strongly diluted when transferred from Bt maize to S. frugiperda
and was not detected in larvae, cocoons or adults of C. marginiventris.
These results refute previous reports of C. marginiventris being harmed by
Bt proteins.

[link.springer.com]