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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications: Department of Entomology Entomology, Department of 2009 Mitochondrial DNA Variation and Range Expansion in Western Bean Cutworm (Lepidoptera: Noctuidae): No Evidence for a Recent Population Bottleneck Nicholas Miller University of Nebraska-Lincoln, [email protected] David L. Dorhout Iowa State University Marlin E. Rice USDA-ARS, Corn Insects and Crop Genetics Research Unit, Genetics Laboratory, Iowa State University Thomas W. Sappington USDA-ARS, Corn Insects and Crop Genetics Research Unit, Genetics Laboratory, Iowa State University, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/entomologyfacpub Part of the Entomology Commons Miller, Nicholas; Dorhout, David L.; Rice, Marlin E.; and Sappington, Thomas W., "Mitochondrial DNA Variation and Range Expansion in Western Bean Cutworm (Lepidoptera: Noctuidae): No Evidence for a Recent Population Bottleneck" (2009). Faculty Publications: Department of Entomology. 246. https://digitalcommons.unl.edu/entomologyfacpub/246 This Article is brought to you for free and open access by the Entomology, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications: Department of Entomology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. MOLECULAR ECOLOGY AND EVOLUTION Mitochondrial DNA Variation and Range Expansion in Western Bean Cutworm (Lepidoptera: Noctuidae): No Evidence for a Recent Population Bottleneck 1,2 3,4 3 NICHOLAS J. MILLER, DAVID L. DORHOUT, MARLIN E. RICE, AND THOMAS W. SAPPINGTON1 Environ. Entomol. 38(1): 274Ð280 (2009) ABSTRACT The western bean cutworm, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), is a pest of both corn and dry bean crops. At the beginning of the 21st century, the species began to extend its range out of the Great Plains, eastward through the Corn Belt. This rapid range expansion is remarkable because the species distribution had been stable for at least the previous half century, despite the apparent abundance of suitable habitat (i.e., cornÞelds) immediately to the east. We hypothesized that if the western bean cutworm had to overcome a stable barrier to movement before starting the current range expansion, it probably experienced a genetic bottleneck in doing so. To test this hypothesis, variation in the mitochondrial NADH dehydrogenase one (ND1) gene was studied in populations from Wyoming, Nebraska, and Iowa. No differences in overall genetic diversity or haplotype frequencies indicative of a bottleneck were observed between the recently founded populations in Iowa and the established populations in Wyoming and Nebraska. This result suggests that the sudden loss of an ecological exclusion mechanism, allowing the species to move east in appreciable numbers, is more likely to have triggered the range expansion than the surmounting of an extrinsic barrier to movement. The nature of this mechanism is unknown but might be related to recent changes in corn farming practices and technology. KEY WORDS Striacosta albicosta, NADH dehydrogenase 1, biological invasion, Zea mays The western bean cutworm, Striacosta albicosta hosts to P. vulgaris and corn and speculated that S. (Smith) (Lepidoptera: Noctuidae), is a pest of corn albicosta may have evolved on mixed crops of corn and (Zea mays L.) and dry beans (Phaseolus vulgaris L.) beans grown by Native Americans. that is currently expanding its distribution eastward Before the 1950s, S. albicosta was an occasional pest through the Corn Belt of the United States. The spe- of dry beans, largely conÞned to Colorado, Kansas, cies is univoltine and overwinters as a Þfth-stage larva Nebraska, and Idaho (Hoerner 1948). From 1950 on- below the soil surface (Hoerner 1948, Douglass et al. ward, the species became an increasingly destructive 1957). Adults emerge in early July (Hagen 1962) and pest of beans in western Nebraska (Hagen 1963, 1976). oviposit on the leaves of the host plants. On beans, the At about the same time, it was found attacking corn larvae initially feed on the leaves and buds and later crops in southern Idaho (Douglass et al. 1957) and make feeding holes in the young pods (Hoerner 1948). western Nebraska (Hagen 1962). By 1970, S. albicosta On corn, young larvae feed over pollen, anthers, and was established throughout most of Nebraska but re- upper leaf tissue before burrowing into the ears to mained rare east of the Missouri river (Blickenstaff feed on young kernels as fourth and Þfth instars (Ha- and Jolley 1982). The species distribution remained gen 1962). Despite exploiting two very different crop stable for the remainder of the 20th century before species, S. albicosta does not seem to be particularly undergoing a second, more rapid eastward expansion. polyphagous. Blickenstaff and Jolley (1982) studied In 1999, western bean cutworms were found attacking larval development on several bean species, teosinte, experimental plots of corn throughout southwestern and several Solanaceae thought to be alternative hosts Minnesota (OÕRourke and Hutchinson 2000). Al- of S. albicosta. They concluded that all were inferior though the species had been present in South Dakota for many years, it did not begin to cause economic 1 USDAÐARS, CICGRU, Genetics Laboratory, Iowa State Univer- damage until 2000 (Catangui and Berg 2006). Also in sity, Ames, IA 50011. 2000, S. albicosta caused widespread and unexpected 2 Corresponding author, [email protected]. damage to corn crops throughout western Iowa (Rice 3 Department of Entomology, Iowa State University, Ames IA 2000). The species spread into Illinois and Missouri by 50011. 4 Present address: Pioneer Hi-Bred International, Johnston, IA 2004 (Dorhout and Rice 2004, Rice et al. 2004) and 50131. Wisconsin in 2005 (Cullen and Jyuotika 2008), and February 2009 MILLER ET AL.: WESTERN BEAN CUTWORM GENETIC VARIATION 275 Indiana, Michigan, and Ohio by 2006 (Pope 2007, Rice and Pilcher 2007, DiFonzo and Hammond 2008). It is striking that S. albicosta apparently remained largely conÞned to the west of the Missouri River for the last three decades of the 20th century despite an abundance of corn immediately to the east. This sug- gests the existence of some environmental factor that prevented further eastward movement during this pe- riod. Although the nature of such an environmental barrier is unknown, two general categories can be Fig. 1. Locations of western bean cutworm population envisaged. The barrier might be durable and still in samples. The course of the Missouri River is indicated by a existence, as would be expected for a physical land- dashed line. scape feature. Alternatively, the barrier might be tem- porary and have recently disappeared, allowing the present range expansion to begin. A temporary barrier from Wyoming, Nebraska, and Iowa as a Þrst step might consist of, for example, farming practices that toward understanding the processes that have re- make the agricultural environment unsuitable as a sulted in the current, dramatic eastward range expan- habitat but that can change rapidly over wide areas in sion. response to economic or technological developments. Although the identity of any barrier to movement Materials and Methods by S. albicosta is unknown, some clues as to its nature may be obtained by comparing genetic diversity in Sampling and DNA Extraction. Male S. albicosta populations that predate the current range expansion were collected in July 2006 from Goshen County, WY (i.e., west of the Missouri River) and new populations (42.246Њ N, 104.486Њ W); Dawson County, NE (40.972Њ further east. If S. albicosta had to cross a durable N, 100.361Њ W); Audubon County, IA (41.697Њ N, barrier before starting the current range expansion, it 95.214Њ W), and Iowa County, IA (41.866Њ N, 92.337Њ is unlikely that it did so spontaneously in large num- W) (Fig. 1). At each location, adult males were cap- bers. Thus, we may expect that there was a population tured in two traps placed 25 m apart. Traps were bottleneck at the beginning of the range expansion fashioned from 3.8-liter plastic milk containers into resulting in genetic founder effects associated with a which four Ϸ60-cm2 holes had been cut leaving a 6-cm small number of colonizers. If so, younger eastern deep reservoir that was Þlled with a 4:1 mixture of populations are expected to be less genetically diverse water and ethylene glycol (Seymour et al. 1998, Dor- than older populations. In addition, signiÞcant allele hout and Rice 2008). Each trap was mounted on a pole, frequency differences would be expected between 1.2 m above ground level, and was baited with an S. younger and older populations as a result of acceler- albicosta sex pheromone lure (Scentry Biologicals, ated genetic drift during the bottleneck. However, if Billings, MT). Traps were left in the Þeld for 10 d a temporary barrier recently dissipated, allowing large during the Þrst 2 wk of July, after which dead males numbers of S. albicosta to migrate east, a bottleneck were removed from the ethylene glycol solution and would not be expected. Under this scenario, younger stored at Ϫ20ЊC. populations would exhibit similar levels of genetic DNA was extracted from the thoraxes of individual diversity to older populations, and no unusually high S. albicosta using a modiÞed CTAB (Cetyl trimethyl- allele frequency differences would be expected be- ammonium bromide) method (Marcon

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