Molecular characterization of Spodoptera frugiperda resistance to Bt corn

Transgenic corn varieties producing insecticidal toxins from Bacillus thuringiensis (Bt) represent more than 60% of the US corn acreage.  This high level of adoption represents an increased selection pressure for the development of insect resistance.  High levels of field-evolved resistance to Bt corn expressing the Cry1Fa toxin were previously reported for Spodoptera frugiperda in Puerto Rico.  We report on the molecular characterization of resistance in a strain of S. frugiperda originated from individuals collected from corn fields in Puerto Rico.  Quantitative determination of transcript levels confirmed that alkaline phosphatase (ALP) and aminopeptidase-N (APNs) genes were significatively down-regulated in resistant compared to susceptible S. frugiperda larvae.  This down-regulation was associated with reduced Cry1Fa toxin binding and resistance to Bt corn producing this toxin.  We describe research aimed at characterizing the mechanism responsible for this down-regulation and testing the role of reduced ALP and APN expression in resistance to Bt corn.