Location: Corn Insects and Crop Genetics Research
Project Number: 5030-22000-018-03-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2014
End Date: Apr 30, 2018
Obtain demographic estimates of western corn rootworm (WCR) (Diabrotica virgifera virgifera) adult population densities from 20 locations in eastern Colorado and western Kansas along two transects, and population genetics estimates of gene flow and isolation by distance. This information will be used to calculate Wright's neighborhood area for this species, the radius of which constitutes the normal spatial scale of dispersal from the natal field.
The overall goal of the project is to use molecular methods, fields studies and two different models to address data gaps in WCR biology, particularly related to adult dispersal, that are critical in providing reliable models to address resistance, remediation and the optimal use of compromised traits. This will be accomplished through 4 objectives: 1) Estimate inter-field movement via genetic differentiation. 2) Estimate components of intra- and inter-field movement through detection of ovipositional patterns and direct measurement. 3) Interpret and integrate empirical data to generate model parameters. 4) Generate models for remediation and deployment strategies, incorporating dispersal parameters. ARS, in close cooperation with Iowa State Univ. collaborators, will be specifically responsible for conduct and completion of Objective 1. We will determine the radius of Wright's genetic neighborhood area for WCR, representing normal lifetime dispersal distance. The main activities will include adult population sampling, and population genetics analyses in a continuous distribution of WCR in northern Colorado where genetic differentiation occurs. Critical to this objective is the estimate of genetic differentiation among populations. WCR only expanded it's range into the Midwest in the last 40-70 years, and previous studies indicate that this expansion resulted in populations with little genetic differentiation. Preliminary experiments using 800 new Single Nucleotide Polymorphism (SNP) markers have shown that populations are significantly differentiated in its original home range in western Kansas and eastern Colorado, where the range expansion is not a factor. Populations will therefore be sampled along two transects in Colorado and Kansas for both census demography data and for genetic analysis. This will allow calculations of rate of gene flow between populations separated by various distances, and to calculate genetic neighborhood area. Knowing the radius of the neighborhood area of WCR within the larger continuous distribution is important in predicting rate of development of resistance to transgenic Bt corn and the rate of spread after it develops, because conceptually it is a measure of the average distance genes move per generation. WCR resistance to Bt corn is being documented in the field over ever-growing areas of the Corn Belt, and mitigation depends critically on understanding dispersal distances and gene flow patterns. To obtain the necessary demographic population density information, we will sample 3 fields each at 10 locations along each of the two transects (60 samples total). Results of the models will be used to determine a preferred strategy to sustainably deploy transgenic Bt varieties for control of western corn rootworm, prevention of resistance development, and mitigation of resistance already detected.