Host-associated Genetic Differentiation in Fall Armyworm (Lepidoptera: Noctuidae): a Sibling Species Complex?

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Abstract
Fall armyworm, Spodoptera frugiperda (J. E. Smith), is a major agricultural pest of many crops throughout its distribution in the Western Hemisphere. Its polyphagy has been attributed to a lack of dietary specialization. Results presented here suggest that this is not the case and that the fall armyworm is composed of genetically differentiated strains, each exhibiting different host specificity. At least two host strains exist, one that feeds on corn and another on rice and Bermuda grass. Collections from Bermuda grass in Louisiana and rice in Puerto Rico are genetically identical at 11 polymorphic enzyme loci and are significantly different from populations on corn in Puerto Rico and Louisiana at 5 loci. In a split progeny experiment in which offspring from the two host strains were reared on both corn and rice, the host plant upon which larvae fed had no influence on the genotype of survivors. Thus, genetic differences are not caused by feeding on the host plant but are inherent in the strains. If the two strains are determined to be reproductively isolated, as implicated by preliminary hybridization data, then at least two sibling species exist.