Mitochondrial DNA Variation and Range Expansion in Western Bean Cutworm (Lepidoptera: Noctuidae): No Evidence for a Recent Population Bottleneck

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., cornfields) 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.

Population Genetics of the Western Bean Cutworm (Lepidoptera: Noctuidae) Across the United States

“…It is possible that a genetically diverse group, perhaps from multiple locations, colonized the new territory. Like Miller et al (2009) we conclude that as there is no evidence of a bottleneck effect; therefore, it is unlikely that S. albicosta evolved the ability to overcome some barrier, but rather that there was a previous barrier to population expansion that is no longer present.…”

“…Eastern locations also do not exhibit more genetic isolation from western locations than western locations do from one another. Miller et al (2009) came to a similar conclusion by analyzing differences in the NADH dehydrogenase gene in the mitochondrial DNA of four subpopulations of S. albicosta from Wyoming, Nebraska, and Iowa. Their study revealed no signiÞcant heterogeneity between subpopulations, and they rejected the hypothesis that S. albicosta subpopulations in the east are subject to a bottleneck effect.…”

“…A recent genetic analysis of S. albicosta subpopulations from Wyoming, Nebraska, and Iowa revealed no evidence of a bottleneck effect, suggesting that the range expansion is more likely because of ecological factors than due to a founder population (Miller et al 2009). Dorhout and Rice (2010) hypothesized that the S. albicosta has expanded eastward in response to a niche recently opened by the widespread planting of maize containing the Cry1Ab protein.…”

“…Although existing evidence indicates no genetic bottleneck for S. albicosta (Miller et al 2009), the recent expansion of S. albicosta populations and the advent of companies producing genetically modiÞed corn with traits effective against this pest necessitates better understanding of the genetics and gene ßow of S. albicosta populations. Knowledge of the amount of variation and gene ßow among populations is important in managing resistance to control methods.…”

Degree-Day Prediction Models for the Flight Phenology of Western Bean Cutworm (Lepidoptera: Noctuidae) Assessed with the Concordance Correlation Coefficient

“…In recent years, significant western bean cutworm infestations have been observed in corn beyond the previously described range in the west-central United States (Miller et al 2009). S. albicosta has been documented north to Iowa and southern Minnesota, east to Massachusetts, and south into Mexico (O'Rourke and Hutchison 2000, Rice 2000, Michel et al 2010, PSU Pestwatch 2014.…”