Population Genetics of the Western Bean Cutworm (Striacosta albicosta Smith) Across the United States

The western bean cutworm, Striacosta albicosta (Smith), is a secondary pest of maize (Zea mays L.) and dry beans (Phaseolus vulgaris L.) in the western United States. Recently, this insect has undergone a major territory expansion into the eastern US and has become a pest throughout much of the Corn Belt. This study was instigated to examine the population genetics of this pest to facilitate control and resistance management, as well as to shed light on the current habitat expansion. To this end, western bean cutworm individuals were collected from 28 different locations across the traditional and expanded range and amplified fragment length polymorphism analysis was conducted to assess genetic variability. A total of 90 markers were analyzed, encompassing >90% of genetic variation. Gst across all locations was low (Gst = 0.0385), while gene flow among all locations was high (Nm = 12.929). AMOVA analysis revealed that the majority of genetic variation is within locations (54%), suggesting interbreeding between locations. The Mantel test revealed no correlation between geographic and genetic distance (n = 600, r = 0.036553, p = 0.226000). Locations sampled in the eastern US did not exhibit any reduction in genetic variation in comparison to locations sampled in the western US, so I conclude that no bottleneck event has occurred. These results suggest that there is enough gene flow between geographically distant locations to prevent genetic isolation from occurring. It is also possible that the western bean cutworm in the eastern US is too recently established to exhibit any genetic differentiation from the western US. I am indebted to those who helped collect samples for this project, including Concord. I am particularly grateful to the students and staff of the Department of Entomology for making graduate school an enjoyable experience. I would like to thank my labmates Bamphitli Tirosele, Difabachew Belay, and especially Kate Kneeland for all their help. I would not be where I am today without the assistance of my family. I am thankful not only for their financial support throughout these long years of school, but also for their love and encouragement. I certainly would not have obtained a Ph.D without the solid educational foundation I received at home. Most importantly, I thank my husband for his technical expertise, love, and unwavering support. This Ph.D is for him.