Genetic evidence of bimodal dispersal behavior among adult western corn rootworm (Coleoptera: Chrysomelidae)

Authors: KIM, KYUNG SEOK - Iowa State University; Coates, Brad; NASON, JOHN - Iowa State University; CAPRIO, MICHAEL - Mississippi State University; SPENCER, JOSEPH - University Of Illinois; FRIEDENBERG, NICHOLAS - Applied Biomathematics; Sappington, Thomas

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2025
Publication Date: 5/30/2025
Citation: Kim, K., Coates, B.S., Nason, J.D., Caprio, M.A., Spencer, J.L., Friedenberg, N.A., Sappington, T.W. 2025. Genetic evidence of bimodal dispersal behavior among adult western corn rootworm (Coleoptera: Chrysomelidae). Environmental Entomology. p. 1-17. https://doi.org/10.1093/ee/nvaf046.
DOI: https://doi.org/10.1093/ee/nvaf046

Interpretive Summary: The western corn rootworm (WCR) is the most destructive insect pest of corn in the United States, causing about $2-billion in losses each year. It is very difficult to manage because of its ability to develop resistance to many forms of control, including transgenic Bt-corn used by many farmers. Understanding the patterns and distances that adults fly in their lifetime is critical to improving pest management and resistance management strategies. However, a holistic understanding of adult WCR movement has remained elusive because of conflicting evidence of short- and long-distance lifetime dispersal, a type of dilemma in ecology called Reid’s Paradox. To solve this dilemma, we analyzed genetic markers in WCR from 14 populations to obtain estimates of gene exchange between them, which provides an indirect way to estimate dispersal distances. The results indicated movement can occur over long distances, at least 175 miles. This is much further than direct observations in the field suggest that WCR flies during its life, a similar type of dilemma often encountered in animal ecology called Slatikin's Paradox. In another type of analysis, we combined gene flow estimates with sampling of WCR population density to estimate typical lifetime dispersal, which was only about 580 feet. The widely differing, yet well-supported estimates of dispersal distance are actually the key to solving these paradoxes. Taken together, the evidence is clear that most individual WCR do not travel very far in their lifetime, often laying eggs in the same field they emerged in, while other individuals are prone to take long flights of many miles before leaving offspring. In other words, our research shows that in any population of WCR adults there are distinct behavioral types of individuals, "residents" and "dispersers". This information will be used by university and government scientists to improve models of WCR population dynamics and to devise better methods to manage WCR populations in the agricultural landscape.

Technical Abstract: A coherent understanding of adult western corn rootworm (Diabrotica virgifera virgifera) movement ecology has remained elusive because of conflicting evidence of short- and long-distance lifetime dispersal, a type of dilemma called Reid’s Paradox. Previous attempts to resolve this paradox using population genetics strategies have been hindered by the lack of gene flow-genetic drift equilibrium in much of North America related to this species’ recent range expansion out of the Great Plains across the Corn Belt. We used 2,036 single-nucleotide polymorphism (SNP) markers to assess population differentiation and obtain indirect estimates of dispersal distances. In this study, however, samples were taken along transects in northeastern Colorado and western Kansas where D. v. virgifera has been resident for >175 years. Significant isolation by distance (IBD) and pairwise FST estimates across 14 locations suggest these populations are at or near gene flow-genetic drift equilibrium. Low FST values and shallow IBD slopes suggest gene flow over longer distances (280 km) than supported by many direct measures of dispersal distance, another type of dilemma known as Slatkin’s Paradox. Indeed, based on estimates of adult population density and Wright’s neighborhood area at each location, estimated lifetime dispersal by diffusion was very low, only 174 m. Together, our genetic evidence and evidence from earlier studies suggest that D. v. virgifera populations consist of two behavioral phenotypes, one that engages in long-distance dispersal and one that disperses only locally by diffusion, resulting in bimodal dispersal distances and resolution of Reid's and Slatkin's paradoxes.