F2 screening for resistance to pyramided Bacillus thuringiensis maize in Louisiana and Florida populations of Spodoptera frugiperda (Lepidoptera: Noctuidae)

F₂ screening procedures were developed for detecting rare resistance alleles to transgenic Bacillus thuringiensis maize in field populations of the fall armyworm, Spodoptera Frugiperda (J.E. Smith). The F₂ screening method includes 1) collecting larvae from fields; 2) rearing field-collected larvae to pupal stage and sexing all pupae within a location; 3) establishing F₂ two-parent family lines; 4) detecting Bt resistance alleles in each F₂ family line on Bt maize leaf tissues; 5) confirming Bt resistance for potential positive family-lines on whole Bt maize plants in the greenhouse; and 6) estimating Bt resistance allele frequencies. During 2011, a total of ≈150 two parental F₂ family lines were established from larvae of S. frugiperda collected from three locations in Louisiana and Florida. These family lines were screened for resistance to three recently commercialized pyramided maize traits: Agrisure^® Viptera^TM 3111, Genuity^® VT Double Pro^TM, and Genuity^® SmartStax^®. All these three Bt maize traits were effective against the three field insect populations. None of the 150 F₂ family lines was identified to possess major resistance alleles to any of the three Bt maize traits. The joint resistance allele frequency with 95% probability in the three populations of S. frugiperda was estimated to be <0.0049 to the pyramided Bt maize traits. The results of the F₂ screen suggest that resistance allele frequency to the three pyramided maize traits appears to be very low in field populations of S. frugiperda in the southern region of the United States.