Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2016
Publication Date: 3/16/2016
Citation: Nagoshi, R.N., Meagher Jr, R.L. 2016. Using intron sequence comparisons in the triose-phosphate isomerase gene to study the divergence of the fall armyworm host strains. Insect Molecular Biology. 25(3):324-337.
Interpretive Summary: The migratory pest fall armyworm (Spodoptera frugiperda) is a significant pest of corn, cotton, grasses, and rice in North and South America and the Caribbean, and is the number one pest of sweet corn in south Florida. The fall armyworm appears to be undergoing speciation to produce two subpopulations that differ in their choice of host plants. Researchers at the USDA Agriculture Research Service, Center for Medical, Veterinary and Agricultural Entomology, in Gainesville, Florida, used genetic markers to identify the diverging “rice strain” and “corn strain” that are morphologically indistinguishable. In this study, DNA sequences from a specific sex chromosome gene are examined to develop new genetic strategies for strain identification and to gain insights into the genetic relationships of the two subpopulations. The results confirm that the DNA sequence comparisons are an effective and efficient approach to study diverging fall armyworm populations.
Technical Abstract: The Noctuid moth, Spodoptera frugiperda (the fall armyworm), is endemic to the Western Hemisphere and appears to be undergoing sympatric speciation to produce two subpopulations that differ in their choice of host plants. The diverging “rice strain” and “corn strain” are morphologically indistinguishable, requiring the use of genetic markers to identify the two groups. Because fall armyworm is a major pest of corn and several other agricultural crops, characterizing the strains and identifying their associated hosts has significant economic consequences, particularly with respect to predicting and mitigating infestations. In this study, EPIC (Exon-Priming Intron-Crossing) methodology is used to compare the intron sequences from the triose-phosphate isomerase (Tpi) gene in order to develop new genetic strategies for strain identification and to gain insights into the genetic relationships of the two subpopulations. A number of new strain specific haplotypes are described that should facilitate the characterization of fall armyworm field populations associated with different host plants. Comparisons of genetic diversity between the strains support the contention that directional interstrain mating is occurring in the wild and provides evidence that the corn strain is undergoing active selection. Comparisons of the types and frequencies of polymorphisms indicate that each intron undergoes different patterns of mutation that in some cases corresponds to host plant preferences. The results confirm that intron sequence comparisons are an effective and efficient approach to study fall armyworm population genetics.