A next-generation sequencing approach for detecting field-evolved resistance to Bt crops

Heliothis virescens is an historically important pest of cotton.  For nearly two decades, H. virescens populations have been successfully managed by transgenic cotton cultivars that express Bt toxin.  Yet H. virescens infestations persist in other cropping systems.  This suggests that Bt cotton cultivars impose strong selection pressure on H. virescens to seek alternative hosts.  To test this hypothesis, we collected H. virescens adults from pheromone-baited traps across multiple years (1997-2012).  Collections took place in Louisiana and Texas, two regions with varying levels of Bt adoption.  Genomic DNA sequences of field-collected individuals were compared by location and year using RAD-enabled sequencing and population genomics techniques.  This molecular approach, known as "reverse ecology", can be used to detect genomic regions that are targets of natural selection and important for adaptation.  Our results are discussed within the context of behavioral adaptation by insects to management practices.