Node-Injury Scale to Evaluate Root Injury by Corn Rootworms (Coleoptera: Chrysomelidae)

Abstract

Corn rootworm larval feeding on corn roots can significantly reduce grain yield by interfering with photosynthetic rates, limiting the uptake of water and nutrients, and by increasing the plant's susceptibility to lodging. Of the techniques developed to measure the efficacy of corn rootworm larval control tactics, root damage ratings have generally been adopted as the standard because sampling roots is relatively efficient. Historically, the primary scales used for scoring root injury from corn rootworm larval feeding have been the 1-6 and 1-9 scales. A critical deficiency of those scales, however, is that each increase in a root-rating score does not reflect a linear increase in the actual amount of injury to the root system. This results in injury scores that are expressed qualitatively. We developed the node-injury scale to more accurately quantify corn rootworm larval injury based on the proportion of nodal roots that contain feeding injury. With the node-injury scale, the relationship between the numerical scale and the amount of root injury is linear and intuitive. In this article, we describe the node-injury scale, discuss sampling issues to consider when using the scale, and suggest the minimum node-injury score that causes economic damage under varying degrees of environmental stress.

Field-evolved resistance by western corn rootworm to multipleBacillus thuringiensistoxins in transgenic maize

“…For each field, the presence of rootworm-active Bt toxin in each maize plant sampled was verified based on ELISA (Envirologix). Rootworm injury was quantified based on the 0-3 node-injury scale (34), and any plants that did not test positive for Bt toxin were not evaluated for root injury (6 of 180 plants). For fields with an average root injury of greater than one node, we mapped the county within Iowa that contained the field by plotting GPS coordinates in Google Earth (Google, Inc.) and then manually transferring the location, accurate to the level of an individual county, to a map of Iowa (Iowa Department of Natural Resources, Iowa Geological Survey).…”

Evidence of Resistance to Cry34/35Ab1 Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae): Root Injury in the Field and Larval Survival in Plant-Based Bioassays

“…The presence or absence of rootworm active Bt toxin in each corn plant was tested with ELISA using a kit (Envirologix, Portland, ME), and for the majority of fields, a mixture of Bt and non-Bt corn plants were sampled (Table 1). Soil was washed from roots, and roots were rated for rootworm feeding injury following the 0 to 3 node injury scale of Oleson et al (2005).…”

“…c Mean 6 SD for root injury on a 0 to 3 node injury scale (Oleson et al 2005). Numbers in parentheses are sample sizes.…”

Effect of Bt Maize and Soil Insecticides on Yield, Injury, and Rootworm Survival: Implications for Resistance Management

“…In total, 120 plants were sampled at each location during each year (5 plants per eight-row treatment plot ϫ 2 maize hybrids ϫ 3 insecticide treatments ϫ 4 blocks). Injury was scored based on a node-injury scale (Oleson et al 2005) that ranges from zero (no feeding injury) to three nodes of root tissue injured (heavy feeding injury). The center four rows of each eight-row plot were harvested, and mass of grain was converted to metric tons per ha at 15.5% moisture (United States no.…”