Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 8, 2008
Publication Date: November 1, 2008
Citation: Nagoshi, R.N., Armstrong, J.S., Silvie, P., Meagher Jr, R.L. 2008. Structure and distribution of a strain-biased tandem repeat element in fall armyworm (Lepidoptera: Noctuidae) populations in Florida, Texas, and Brazil. Annals of the Entomological Society of America. 101:1112-1120. Interpretive Summary: Fall armyworm, is a significant pest of maize and turf grasses. Two strains exist that display significant differences in such important traits as plant host choice and pesticide susceptibility, but because they are morphologically identical relatively little is known about their behavior in the wild. In this study scientists at the Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL, optimized molecular methods for detecting a strain-specific genetic marker in order to demonstrate its existence in fall armyworm populations throughout most of the western hemisphere. These results demonstrated that the distribution of this marker between strains has remained relatively unchanged over time and geography, indicating at least partial barriers to the formation of successful hybrids. Such barriers have important implications in our understanding of fall armyworm population movement and might have utility in directing novel biological control methods.
Technical Abstract: Fall armyworm is a major economic pest throughout the Western Hemisphere. There exist two morphologically identical but genetically distinct strains (corn-strain and rice-strain) that differ in their host plant preferences. These can be distinguished by polymorphisms in the mitochondrial Cytochrome oxidase I gene. There is also a tandem-repeat genetic element called FR that is found in large sex-linked clusters primarily in the rice strain, as characterized by sampling of fall armyworm populations in the southeastern United States. It was recently shown that the FR element is also present in Brazil, where it shows a similar strain-biased distribution. In this paper, the analysis of FR was extended to populations in southern Texas, one of the principle overwintering locations for fall armyworm that infests the continental United States. DNA sequence analysis and an optimized PCR-based method demonstrated that FR sequences are present in Texas and shows the same distribution pattern as observed in Florida. Furthermore, the distribution of FR in Florida has remained relatively unchanged over a four year period, suggestive of polymorphic equilibrium and the existence of at least partial barriers to the generation or survival of interstrain hybrids. The implications of these finding on our understanding of interstrain mating behavior and the utility of the modified detection method to study fall armyworm populations are discussed.