Risk Assessment of Cry1A.105-resistant Fall Armyworm to Transgenic Corn Containing Single or Pyramided Bacillus thuringiensis Genes

Resistance evolution in pest populations is a great threat to the sustainable use of transgenic Bt crops. The fall armyworm (FAW), Spodoptera frugiperda, is a target of transgenic corn expressing Bt proteins. Two Cry1A.105-resistant FAW populations (RR32 and RR72) were established using an F₂ screen of field populations from Florida in 2011. The objective of this study is to determine and compare the inheritance and fitness costs of Cry1A.105 resistance in RR32 and RR72 and to evaluate the survival and plant injury of Cry1A.105-susceptibile, -resistant (RR32 and RR72), and -heterozygous FAW populations on four non-Bt and seven Bt corn hybrids/lines. These Bt corn products included four single-gene Bt corn (Cry1A.105, Cry2Ab2, Cry1F or Cry1Ab) and three pyramided Bt corn traits (Genuity^® VT Double Pro^TM, SmartStax^TM, and Agrisure^® Viptera^TM 3111). Cry1A.105 resistance was inherited as a single autosomal and non-recessive gene in RR32 and RR72, while no fitness costs were associated with the resistance in both populations. RR32 and RR72 were highly cross-resistant to Cry1F, but not to Cry2Ab2. All three pyramided Bt corn traits were highly effective against the Cry1A.105-resistant FAW. The cross-resistance between Cry1F and Cry1A.105 could create a great challenge in managing resistance of FAW to Bt crops.