Genetic studies of fall armyworm indicate a new introduction into Africa and identify limits to its migratory behavior

Abstract

The fall armyworm, Spodoptera frugiperda (J.E. Smith) is native to the Americas and a major pest of corn and several other crops of economic importance. The species has characteristics that make it of particular concern as an invasive pest, including broad host range, long-distance migration behavior, and a propensity for field-evolved pesticide resistance. The discovery of fall armyworm in western Africa in 2016 was followed by what was apparently a remarkably rapid spread throughout sub-Saharan Africa by 2018, causing economic damage estimated in the tens of billions USD and threatening the food security of the continent. Understanding the history of the fall armyworm invasion of Africa and the genetic composition of the African populations is critical to assessing the risk posed to different crop types, the development of effective mitigation strategies, and to make Africa less vulnerable to future invasions of migratory moth pests. This paper tested and expanded on previous studies by combining data from 22 sub-Saharan nations during the period from 2016 to 2019. The results support initial descriptions of the fall armyworm invasion, including the near absence of the strain that prefers rice, millet, and pasture grasses, while providing additional evidence that the magnitude and extent of FAW natural migration on the continent is more limited than expected. The results also show that a second entry of fall armyworm likely occurred in western Africa from a source different than that of the original introduction. These findings indicate that western Africa continues to be at high risk of future introductions of FAW, which could complicate mitigation efforts.

Resistance bioassays and allele characterisation inform analysis ofSpodoptera frugiperda(Lepidoptera: Noctuidae) introduction pathways in Asia and Australia

“…frugiperda (Nagoshi et al 2022), in populations from China (Jiang et al 2022), in Africa (e.g., Benin vs. Malawi; , and in, e.g., Australia, Malaysia, and Myanmar vs. China populations (Rane et al 2022),…”

“…Novel introductions leading to unique population structure has been reported for western African S. frugiperda (Nagoshi et al 2022), in populations from China (Jiang et al 2022), in Africa (e.g., Benin vs. Malawi; Tay et al 2022a), and in, e.g., Australia, Malaysia, and Myanmar vs. China populations (Rane et al 2022), suggesting that the widely anticipated long distance migration of S. frugiperda especially in the invasive range could likely be less and may be impacted by localised ecological and climatic determinants (Tay et al 2022b).…”

“…Novel introductions leading to unique population structure has been reported for western African S. frugiperda (Nagoshi et al 2022), in populations from China (Jiang et al 2022), in Africa (e.g., Benin vs. Malawi; Tay et al 2022a), and in, e.g., Australia, Malaysia, and Myanmar vs. China populations (Rane et al 2022), suggesting that the widely anticipated long distance migration of S. frugiperda especially in the invasive range could likely be less and may be impacted by localised ecological and climatic determinants (Tay et al 2022b). Factors impacting the founding for the two Australian populations (e.g., founding number (i.e., involving one/few individuals vs. many); gene flow dynamics at spatial and temporal scales, and frequencies and impact from potential novel and on-going introductions) used in our bioassay studies is at present unknown.…”

Population genomics of fall armyworm in Brazil and Argentina revealed by Genotyping-by- Sequencing and implications for pest management

“…Long distance migration enables FAW populations to travel from Southern Texas and Florida up to Canada, a distance of nearly 2500 km, in less than three months 11,35 . Therefore given its strong ight performance, we can hypothesize that FAW is also performing long distance migration within Brazil su cient to keep populations homogeneous within each host strain.…”

Global genomic analysis reveals the genetic origin and secondary invasion of fall armyworm in the Eastern hemisphere

“…Studies based on molecular markers indicated that the invasive FAW originated from a single source with a high similarity to samples from Florida and the Greater Antilles (Nagoshi et al 2017;Nagoshi et al 2020), while other studies using genome-wide analyses supported multiple introductions of FAW into Africa and suggested South America as a potential source of FAW invasion into Africa (Nagoshi et al 2022;Tay et al 2022). In the Western hemisphere, the FAW has undergone a divergence into two "strains", a rice-strain and a corn-.…”