Characterization of the field-evolved resistance mechanism to Bt corn in Spodoptera frugiperda

Cry proteins synthesized by the bacterium Bacillus thuringiensis (Bt) are pore forming toxins which are either produced by transgenic plants (Bt crops) or included in spray formulations to control agricultural insect pests. The extensive adoption of Bt crops represents high pressure for selection of resistance in target insect pests. Spodoptera frugiperda is a voracious polyphagous pest of economically important crops including corn, cotton and rice. Populations of S. frugiperda developed resistance to transgenic corn producing the Cry1Fa Bt insecticidal protein. In our previous research we have shown that resistance in the 456 strain of S. frugiperda developed from field-collected individuals from Puerto Rico is associated to reduced Cry1Fa and Cry1A binding and reduced expression of selected alkaline phosphatase genes. In this work we present our findings towards elucidating the mechanism responsible for resistance in the 456 strain as well as its existence in resistant S. frugiperda collected in the southeastern USA.