ARS | Publication request: Population Genetics of the Western Bean Cutworm Striacosta albicosta Smith (Lepidoptera: Noctuidae) Across the United States

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 29, 2012
Publication Date: N/A

Interpretive Summary: Western bean cutworms have recently been elevated from secondary to primary pest of corn and dry beans in the U.S. This may be due, in part, to management practices in the use of corn genetically engineered to express a toxin effective against other pests as well as reduced tillage practices in corn fields. The common use of genetically modified corn may have also facilitated the range expansion of the western bean cutworm from the western to eastern U.S. After sampling western bean cutworms from 28 locations across its current range we used the molecular genetic technique of amplified fragment length polymorphism to investigate its population genetics. Analysis of the data showed genetic variation to be highest within sub-populations but variation among sub-populations indicated some genetic isolation. Generally, genetic variation in the western bean cutworms from the ‘new’ eastern range was similar to the genetic variation of sub-populations from the ‘historic’ western range. This suggests that the movement of western bean cutworms has been uni-directional, from west to east, and no genetic ‘bottlenecks’ have occurred. This baseline genetic information will be useful when comparing populations of western bean cutworms in the future, especially if resistance to farmer applied management practices begins to occur.

Technical Abstract: 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. 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 moderate (Gst = 0.5032). AMOVA revealed that the majority of genetic variation was within locations (54%) and among locations within groups (45%) indicating some genetic structuring of subpopulations. The Mantel test revealed no correlation between geographic and genetic distance (n = 600, r = 0.0365, p = 0.2260). Locations sampled in the eastern US did not exhibit any reduction in genetic variation in comparison to locations sampled in the western US, so we conclude that no bottleneck event has occurred. These results suggest that western bean cutworm migration is uni-directional, from the western US to the eastern US.