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Title: ROLE OF EGG DENSITY ON ESTABLISHMENT AND PLANT-TO-PLANT MOVEMENT BY WESTERN CORN ROOTWORM LARVAE (COLEOPTERA: CHRYSOMELIDAE)

Author
item Hibbard, Bruce
item HIGDON, MATTHEW - UNIV OF MISSOURI
item DURAN, DANIEL - UNIV OF MISSOURI
item SCHWEIKERT, YVONNE - UNIV OF MISSOURI
item ELLERSIECK, MARK - UNIV OF MISSOURI

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2004
Publication Date: 6/1/2004
Citation: Hibbard, B.E., Higdon, M.L., Duran, D.P., Schweikert, Y.M., Ellersieck, M.R. 2004. Role of egg density on establishment and plant-to-plant movement by western corn rootworm larvae (coleoptera: chrysomelidae). Journal of Economic Entomology. 97(3):871-882.

Interpretive Summary: The registration of transgenic corn with resistance to corn rootworm larval feeding offers a viable alternative to insecticides for managing the most economically important insect pests of corn. Maintaining susceptibility to transgenic crops (resistance management) is in the interest of growers, the Environmental Protection Agency, and industry, but requires an understanding of corn rootworm biology (such as factors involved in larval establishment and movement) that does not currently exist. The effect of egg density on establishment and dispersal of larvae of the western corn rootworm was evaluated in a three-year field study with six egg densities and six sample dates each year. On each sample date, four replications of each egg density were sampled for both larval recovery and plant damage. Initial establishment on a corn plant was not density-dependent. Plant damage and, secondarily, subsequent post-establishment larval movement were density-dependent. Very little damage and post-establishment movement occurred at lower infestation levels, but significant damage and movement occurred at higher infestation rates. Movement generally occurred at a similar time as significant plant damage and not at initial establishment, so timing of movement appeared to be motivated by available food resources rather than crowding. At the highest infestation level in 2001, significant movement across the 0.76 m row and three plants down the row was detected. This information will be important to seed companies, the Environmental Protection Agency, and modelers in their attempts to develop resistance management plans for transgenic corn.

Technical Abstract: The effect of egg density on establishment and dispersal of larvae of the western corn rootworm, Diabrotica virgifera vifgifera LeConte, was evaluated in a 3-year field study. Viable egg levels of 100, 200, 400, 800, and 1600 eggs per plant were evaluated in 2000, 2001, and 2002. A 3200 viable egg level was added in 2001 and 2002. All eggs were infested on one plant per subplot in a field that was planted to soybeans (Glycine max L.) in the previous year. For each subplot, the infested plant, three plants down the row, the closest plant in the adjacent row of the plot, and control plant at least 1.5 m from any infested plant (six plants total) were sampled. In 2000, there were five sample dates between egg hatch and pupation, and in 2001 and 2002, there were six sample dates. On each sample date, four replications of each egg density were sampled for both larval recovery and plant damage. Initial establishment on a corn plant was not density-dependent. A similar percentage of larvae was recovered from all infestation rates. Plant damage and, secondarily, subsequent post-establishment larval movement were density-dependent. Very little damage and post-establishment movement occurred at lower infestation levels, but significant damage and movement occurred at higher infestation rates. Movement generally occurred at a similar time as significant plant damage and not at initial establishment, so timing of movement appeared to be motivated by available food resources rather than crowding. At the highest infestation level in 2001, significant movement across the 0.76 m row and three plants down the row was detected. Implications of these data for resistance management plans for Bt crops are discussed.