Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2019
Publication Date: 9/19/2019
Citation: Nagoshi, R.N., Nagoshi, B.Y., Canart, E., Navarrete, B., Solorzano, R., Garces-Carrera, S. 2019. Genetic characterization of fall armyworm (Spodoptera frugiperda) in Ecuador and comparisons with regional populations identify likely migratory relationships. PLoS One. 14(9):e0222332. https://doi.org/10.1371/journal.pone.0222332.
DOI: https://doi.org/10.1371/journal.pone.0222332

Interpretive Summary: The fall armyworm is the primary pest of corn production in South America and in portions of the southeastern United States. Severe outbreaks of fall armyworm have now been reported throughout sub-Saharan Africa and India, posing a significant threat to global agriculture. This makes understanding the migratory behavior of fall armyworm critical to controlling the spread of this pest. Scientists at USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, with colleagues from Ecuador collected and genetically characterized moth specimens from Ecuador and relevant regional locations in the Caribbean and South America. These studies represent the first genetic description of fall armyworm from Ecuador, which lies near a likely migration conduit based on the location of regional trade winds. The results indicate that populations in the northern regions of South America extending from Trinidad and Tobago to the east, Peru to the south west, and Bolivia to the south undergo substantial mixing due to migration and population dispersion. This pattern is consistent with the seasonal wind patterns. In contrast, there is no evidence of substantial introgression of fall armyworm populations from Central America or the Greater Antilles into Ecuador, suggesting that such events may be infrequent. These studies represent an important advance in assessing the likelihood of pest migrations between the two Americas.

Technical Abstract: Fall armyworm, Spodoptera frugiperda (J. E. Smith), is an important agricultural pest native to the Americas that has recently been introduced into the Eastern Hemisphere where it has spread rapidly through most of Africa and much of Asia. The long-term economic consequences of this invasion will depend on how the species and important subpopulations become distributed upon reaching equilibrium, which is expected to be influenced by a number of factors including climate, geography, agricultural practices, and seasonal winds, among others. Much of our understanding of fall armyworm movements have come from mapping genetically defined subpopulations in the Western Hemisphere, particularly in North America where annual long-distance migrations of thousands of kilometers have been documented and modeled. In contrast, fall armyworm mapping in much of the rest of the hemisphere is relatively incomplete, with the northern portion of South America particularly lacking despite its potential importance for understanding fall armyworm migration patterns. Here we describe the first genetic description of fall armyworm from Ecuador, which lies near a likely migration conduit based on the location of regional trade winds. The results were compared with populations from select locations in the Caribbean and South America to investigate the possible migratory relationship between these populations and was further assessed with respect to prevailing wind patterns and the distribution of locations with climate favorable for fall armyworm population establishment and growth.