Evidence for two soybean looper strains in the United States with limited capacity for cross-hybridization

Authors: Nagoshi, Rodney; DAVIS, JEFFREY - Louisiana State University; Meagher, Robert - Rob; MUSSER, F - Mississippi State University; HEAD, GRAHAM - Bayer Cropscience; PORTILLO, HECTOR - Fmc Corporation; TERAN, HENRY - Corteva Agriscience

Submitted to: Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2023
Publication Date: 7/24/2023
Citation: Nagoshi, R.N., Davis, J.A., Meagher Jr, R.L., Musser, F.R., Head, G.P., Portillo, H., Teran, H. 2023. Evidence for two soybean looper strains in the United States with limited capacity for cross-hybridization. Genes. 14:1509. https://doi.org/10.3390/genes14071509.
DOI: https://doi.org/10.3390/genes14071509

Interpretive Summary: The soybean looper is a major pest of soybean in the southeastern United States and is of particular concern because of it's broad host range and capablity of impacting many plant species. Additionally there is evidence of acquired resistance to a number of broad-based pesticides. These traits could reflect multiple and distinct soybean looper populations that differ genetically but have not yet been discovered. The existence of such cryptic population structure could explain the current uncertainties as to where and when the resistance traits are likely to appear. In this study, a geneticist from Gainsville, FL adapted technology used to characterize host strains of the fall armyworm, another moth pest, to soybean looper using specimens obtained from multiple university and industry collaborators. Evidence is presented for at least two distinct populations that have only limited ability to cross-hybridize. The results describe a more complicated population biology in the United States than previously thought with potential relevance to the dispersion of resistance traits and projections of soybean looper migration under different climate scenarios.

Technical Abstract: An economically important pest of soybeans (Glycine max (L.) Merr.) in the southeastern United States is the noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker). It has characteristics that are of particular concern for pest mitigation that include a broad host range, the capacity for annual long-distance flight, and resistance in some populations to important pesticides such as pyrethroids and chitin synthesis inhibitor. The biology of SBL in the United States resembles that of the fellow noctuid fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) a major pest of corn and several other crops. The two species have overlapping host ranges, the same geographical distribution, and nearly identical climate suitability profiles. FAW exhibits population structure in that it can be divided into two groups (host strains) that differ in their host preferences but are broadly sympatric and exhibit incomplete reproductive isolation. The FAW strains are morphologically indistinguishable but can be identified using genetic markers in the Z-linked Triosephosphate isomerase gene (Tpi). There are preliminary indications of at least two SBL populations in South America based on genetic studies, though these have not been replicated. In this paper, strategies used to characterize the FAW strains were applied to SBL to assess the likelihood of population structure in the United States. Evidence is presented for two populations that are defined phylogenetically and can be preliminarily identified by a single polymorphism in the SBL Tpi gene. The populations exhibit evidence of reproductive barriers sufficient to allow a persistent asymmetry in the distribution of mitochondrial haplotypes. The identified molecular markers will facilitate studies characterizing the behaviors of these two populations, with relevance to pest mitigation and efforts to prevent further dispersal of the resistance traits.