Tracking fall armyworm movement across the US using stable isotopes

The fall armyworm, Spodoptera frugiperda, is a highly mobile economic pest endemic to the Western Hemisphere, reportedly traveling up to 1,600 km in a single generation. Because the fall armyworm does not diapause, they are only able to overwinter at two locations in the United States that remain warm enough year round to support continuous generations, South Texas and South Florida. In the spring, moths disperse north from these overwintering locations, making their way into Canada by the end of the season. Evidence of a return migration in this species is currently lacking and all individuals north of the overwintering location are thought to die at the end of the growing season. Thus, their genetic material is removed from the gene pool. This unidirectional migration, or pied piper migration, presents an evolutionary conundrum because any genetic predisposition for dispersal should be removed from the population overtime. Recently, stable hydrogen and oxygen isotopes have proven to be a useful tool for tracking the latitudinal movement of both aquatic and terrestrial insect species. We have initiated a stable isotope analysis to test for evidence of a north to south return migration in Spodoptera frugiperda. Understanding the migratory patterns of this species in the US could facilitate better predictions of population outbreaks, allowing us to stay one step ahead when managing this economic pest.