Submitted to: Nature Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2019
Publication Date: 6/5/2019
Citation: Nagoshi, R.N., Goergen, G., Du Plessis, H., Van Den Berg, J., Meagher Jr, R.L. 2019. Genetic comparisons of fall armyworm populations from 11 countries spanning sub-Saharan Africa provide insights into strain composition and migratory behaviors. Nature Scientific Reports. 9(1):8311. https://doi.org/10.1038/s41598-019-44744-9.
DOI: https://doi.org/10.1038/s41598-019-44744-9

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, posing a significant threat to African agriculture, with the potential for rapid dispersion throughout the hemisphere. Scientists at USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology (Gainesville, Florida) have developed a set of genetic tools to investigate fall armyworm population dynamics. In collaboration with colleagues from the International Institute of Tropical Agriculture (Benin) and the North-West University (South Africa) the genetic marker technology was applied to characterize the fall armyworm infestation in Africa. The genetic analyses provide the first continent-scale descriptions of fall armyworm populations in Africa that will be critical to understanding future movements of this important pest and for future efforts to monitor, predict, and control its spread in the Eastern Hemisphere. The information obtained provides insights into how invasive moths move into new geographic regions that can be applied to model potential similar events that may occur in the United States by related pest species.

Technical Abstract: The recent discovery of fall armyworm (Spodoptera frugiperda, J.E. Smith) throughout sub-Saharan Africa presents a new and significant threat to that continent’s food security. The species is genetically diverse and exhibits several traits in the Western Hemisphere that if transferred to Africa would significantly complicate control efforts. These include a broad host range due in part to two genetically distinct subpopulations, long-distance migratory behavior exhibited in North America, and resistance to multiple pesticides that varies by regional population. Determining which fall armyworm subpopulations are present in Africa is critical to extrapolating likely pest behavior. The current study is an extension of earlier surveys that together combine the collections from 11 nations to produce the first genetic description of fall armyworm populations spanning the sub-Saharan region. The results are most consistent with a single introduction of a small number of haplotypes being responsible for the entirety of the African infestation. Comparisons of haplotype frequencies indicate that natural migration in Africa is not of sufficient magnitude to homogenize populations, with significant differences observed between groups in western and eastern Africa. The types and frequency of haplotypes from all locations continue to identify Florida and the Caribbean regions as the most likely Western Hemisphere origins of the African infestations. In addition, the new data confirm the uncertainty of fall armyworm strain identification in Africa by genetic methods, with the possibility discussed that the African infestation may represent a novel interstrain hybrid population of potentially uncertain behavioral characteristics.