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Title: Genetic differentiation across North America in Heliothis virescens and H. subflexa: A generalist versus a specialist moth

Author
item GROOT, ASTRID - Max Planck Society
item CLASSEN, ALICE - Max Planck Society
item INGLIS, OLIVE - North Carolina State University
item BLANCO, CARLOS - Animal And Plant Health Inspection Service (APHIS)
item Lopez, Juan De Dios
item TERAN VARGAS, ANTONIO - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP)
item SCHAL, COBY - North Carolina State University
item HECKEL, DAVID - Max Planck Society
item SCHOEFL, GERHARD - Hans-Knoll Institute

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2011
Publication Date: 5/26/2011
Citation: Groot, A., Classen, A., Inglis, O., Blanco, C., Lopez, J., Teran Vargas, A., Schal, C., Heckel, D., Schoefl, G. 2011. Genetic differentiation across North America in Heliothis virescens and H. subflexa: A generalist versus a specialist moth. Molecular Ecology. 20(13):2676-2692.

Interpretive Summary: Tobacco budworm and Heliothis subflexa are two closely related species that occur throughout North and South America, but their ecology differs significantly. The tobacco budworm is considered a generalist that feeds on numerous plants including cotton, tobacco, soybean, tomato, sunflower and chickpeas, and H. subflexa is a specialist that feeds exclusively on Physalis including ground cherry and husk tomato. Population genetic analyses of both insect species collected from various locations in the U.S. and Mexico indicated that tobacco budworm was more genetically homogenous than H. subflexa. This study shows that the pest status of tobacco budworm is linked to its ability to feed on numerous plants and disperse to reproduce effectively on these seasonally-available plants. Understanding the effects of mobility and diversity of host plants is critical to the development of effective integrated pest management programs for insects of economic importance.

Technical Abstract: The two moth species Heliothis virescens (F.) and H. subflexa Guenée are closely related, but have vastly different feeding habits. The tobacco budworm, H. virescens, is a generalist and an important pest in many crops in the US, while H. subflexa is a specialist feeding only on plants in the genus Physalis. The population genetic structure of the generalist pest species Heliothis virescens (Hv) (Lepidoptera; Noctuidae) has been assessed in the past, but nothing is known about the population structure of its close relative, the specialist moth Heliothis subflexa (Hs). In this study we assessed whether and how generalist versus specialist life styles are reflected in possible differences in population structures, hence we conducted a comparative population genetic analysis. In Hv 98% of the total variation occurred within populations. The overall differentiation (FST) between regions was 0.006 and even lower between years (0.0039) and hosts (0.0028). Variation among Hv populations was not associated with geographic distance or host plant use, nor were population samples any more similar when closely spaced in time. Analyses of population structure suggest that all individuals form one genetically homogeneous population, except for at most twelve individuals (6%) that diverge from this cluster. Population homogeneity likely results from the high mobility of H. virescens and its generalist feeding behavior. Hs exhibited substantially more population structure. Even though 96% of the total variation was attributable to within-population variability, FST-values between Hs populations were 10 times higher than between Hv populations. Hs populations showed a significant isolation by distance. Analyses of Hs population structure suggest at least two subpopulations and thus some degree of metapopulation structure: North Carolina and the western populations from Texas and eastern and western Mexico. The 2004 Florida population seems to share some ancestry with the 2004 Texas populations. We speculate that the patchy distribution of Physalis – H. subflexa's exclusive food source – contributes to differences in population structure between these closely related species.