Testing for cross-resistance in Spodoptera frugiperda (J. E. Smith) with field-evolved resistance to Bt maize

Testing for cross-resistance in Spodoptera frugiperda (J. E. Smith) with field-evolved resistance to Bt maize Jakka1, S.R.K., Knight1, V.R., and J.L. Jurat-Fuentes1 1 Department of Entomology and Plant Pathology, University of Tennessee, Knoxville (TN) 37996 USA Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an important sporadic insect pest on various agricultural crops in USA and across the world. Transgenic maize producing Cry1Fa or Cry1Ab toxins from Bacillus thuringiensis (Bt) have been used to control S. frugiperda larvae. Evolution of resistance by insect pests is the greatest threat to the continued success of transgenic crops producing Bt toxins. Previous studies showed that S. frugiperda developed resistance to Cry1Fa expressing maize in Puerto Rico. A Cry1Fa-resistant strain of S. frugiperda originally established from field-collected insects from Puerto Rico was used to study potential cross-resistance patterns. Larvae of the resistant S. frugiperda strain exhibited significatively lower mortalities on Cry1Fa expressing maize compared to a susceptible strain. Maize producing Cry1Ab showed limited efficacy on susceptible S. frugiperda and only low levels of cross resistance in the resistant strain. In contrast, data from bioassays with purified Cry1Ca toxin or Dipel ES showed lack of cross-resistance in the Cry1Fa-resistant strain. This cross-resistance phenotype is in agreement with data from Cry toxin binding analyses.