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Annals of the Entomological Society of America (2004) 97, 1034-1044

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Dorothy Pashley Prowell, Margaret McMichael and Jean-François Silvain (2004)
Multilocus genetic analysis of host use, introgression, and speciation in host strains of fall armyworm (Lepidoptera: Noctuidae)
Annals of the Entomological Society of America 97 (5), 1034-1044
Abstract: Two genetically differentiated forms of fall armyworm, Spodoptera frugiperda (J. E. Smith), use different graminaceous host plants, coexist sympatrically throughout their ranges, yet seem to hybridize. To address the taxonomic status of the two forms, determine extent and directionality of hybridization, and examine host specificity, we compiled multilocus genotypes consisting of mitochondrial DNA (mtDNA) haplotypes, an esterase locus, and eight amplified fragment-length polymorphism (AFLP) loci in moths collected across a broad geographic range. Multilocus analyses indicated 16% of individuals sampled were potentially hybrids with a minority being F1 in origin. Analysis of host use indicated asymmetries in host specificity with one strain specific to corn, Zea mays L., and the other strain predominating on pasture grasses and rice, but occasionally using corn. Location of hybrids in nature was biased toward cornfields, the habitat used by both strains. To assess genetic divergence of each gene, we calculated their relative strain discriminating ability. Eight AFLP loci collectively had the greatest discriminating power (98%), followed by a single AFLP locus (93%) and mtDNA (91%). Esterase exhibited 89% discrimination. Esterase is X-linked along with an assortative mating trait, suggesting esterase differentiation may be maintained by association with strain-specific fitness genes. Despite strong discrimination of these genes, most of the genome surveyed was not distinct. Cytonuclear comparisons provided evidence for unidirectional matings consistent with mate preference studies. Collectively, these data support introgressive hybridization between recently evolved species that are not completely reproductively isolated. Genetic divergence in the presence of gene flow may be a common phase in the speciation process, especially in taxa whose ranges have been altered dramatically by humans.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
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Research topic(s) for pests/diseases/weeds:
general biology - morphology - evolution
molecular biology - genes


Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.


Spodoptera frugiperda Grasses/turf/rangeland Puerto Rico
Spodoptera frugiperda Grasses/turf/rangeland Guadeloupe
Spodoptera frugiperda Grasses/turf/rangeland U.S.A. (mid S)
Spodoptera frugiperda Grasses/turf/rangeland U.S.A. (SE)
Spodoptera frugiperda Maize/corn (Zea mays) Puerto Rico
Spodoptera frugiperda Maize/corn (Zea mays) French Guiana
Spodoptera frugiperda Maize/corn (Zea mays) Guadeloupe
Spodoptera frugiperda Maize/corn (Zea mays) U.S.A. (mid S)
Spodoptera frugiperda Maize/corn (Zea mays) U.S.A. (SE)
Spodoptera frugiperda Rice (Oryza) French Guiana