Survival and effective dominance level of a Cry1A.105/Cry2Ab2-dual gene resistant population of Spodoptera frugiperda (JE Smith) on common pyramided Bt corn traits

The fall armyworm, Spodoptera frugiperda (J.E.Smith.), is an important pest that has developed resistance to Bt corn in several countries. In this study, leaf-tissue bioassays and whole-plant tests were conducted to evaluate the performance of a Bt-susceptible (aabb), a Cry1A.105/Cry2Ab2 dual-gene resistant (AABB), and a heterozygous (AaBa) genotypes of S. frugiperda on two non-Bt and five pyramided Bt corn traits. The five Bt corn traits were Genuity (R) VT Double Pro (R) (VT-2P) containing Cry1A.105 and Cry2Ab2 genes, Optimum (R) Intrasect (R) (Intrasect) containing Cry1F and Cry1Ab, Genuity (R) SmartStax (R) (SMT) containing Cry1A.105, Cry2Ab2, and CryiF against lepidopteran pests, Optimum (R) Leptra (R) (Leptra) containing Cry1Ab, Cry1F, and Vip3A, and Trecepta (TM) (Trecepta) containing Cry1A.105, Cry2Ab2, and Vip3A. Larvae of the three genotypes survived well on non-Bt corn, while few aabb survived on Bt corn plants. Survivorship of AABB on Bt leaf tissue was 43.7% for VT-2P, 29.7% for Intrasect, and 47.7% for SMT, and live larvae were recovered from 46.9% of VT-2P, 12.5% of Intrasect, and 21.9% of SMT whole plants. Some AaBb larvae also survived on these three Bt corn traits. In contrast, leaf tissue of Leptra and Trecepta killed all three genotypes, and few larvae survived on whole plants of the two Bt corn traits. The results demonstrated that AABB was highly resistant to VT-2P, and somewhat cross resistant to Intrasect and SMT. The dual-gene resistance in AABB was non-recessive on VT-2P. Pyramided corn traits containing Vip3A were effective against the three genotypes. However, Vip3A in the current pyramided Bt corn traits apparently is the only fully active Bt protein against the Cry1/Cry2-resistant S. frugiperda. More effective resistance management plans are necessary to suppress resistance to Bt crops and sustain the value of these technologies.