Title: Assessing the resolution of haplotype distributions to delineate fall armyworm (Lepidoptera:Noctuidae) migratory behaviors Authors
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2014
Publication Date: N/A
Interpretive Summary: Fall armyworm, a major pest of corn and cotton in the Western Hemisphere, does not survive freezing winters yet annually infest much of the continental USA and Canada. These populations arise from fall armyworm that overwinter in the southern regions of Florida and Texas. Understanding how these overwintering populations annually disperse is important to efforts to predict and control infestations by this pest. A recently developed haplotype ratio method was used to map these migratory pathways.While discrete patterns were observed, there was a region of overlap in the area that included the border of Alabama and Georgia. This overlap provided an opportunity to test the resolution of the haplotype method, specifically whether and to what degree the boundaries between the Texas and Florida migrations can be defined. The capacity to monitor fall armyworm dispersal at this level of detail could allow risk assessments for local infestations and facilitate the use of preemptive mitigation strategies. Extending and expanding these studies over multiple years will allow a more detailed mapping of migratory pathways and the identification of factors that influence the direction and extent of pest migration.
Technical Abstract: Regions of southern Florida and southern Texas (extending into Mexico) provide the overwintering source populations for virtually all fall armyworm infestations affecting the continental U.S. Understanding how these migratory populations annually disperse is important to predict and control infestations by this specific pest and to more generally investigate the environmental factors that influence the long-distance movements of flying insects. The two overwintering locations are associated with differences in the distribution of certain mitochondrial haplotypes that overlap in the region near the border separating the states of Alabama and Georgia. This provided an opportunity to test the resolution of the haplotype method by comparisons between smaller geographical areas and shorter time frames than previously examined. Correspondences were found between trap-capture numbers, fall armyworm strain proportions, and haplotype ratios calculated for individual counties and within season time periods that were generally consistent with expectations, providing confidence that population movements could be accurately inferred. The comparison of haplotype distributions identified a migratory boundary separating the Texas and Florida populations that implicated the eastern edge of the Apalachicola-Chattahoochee-Flint River basin as a physical barrier. Calculations of strain numbers based on genetic markers revealed similarities and differences in strain population dynamics that can be applied to study the migratory behavior of fall armyworm subpopulations. The use of this methodology for the detailed mapping of migratory pathways and the identification of factors that influence the direction and extent of pest migration are discussed.