Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2004
Publication Date: 10/1/2004
Citation: Oyediran, I.O., Hibbard, B.E., Clark, T.L., French, B.W. 2004. Selected grassy weeds as alternate hosts of the northern corn rootworm (coleoptera:chrysomelidae). Environmental Entomology. 33(5):1497-1504. 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 larval use of alternate hosts) that does not currently exist. We evaluated five grass species common in or near corn fields as larval hosts of the northern corn rootworm. The percentage of larvae recovered from barnyard grass, large crabgrass, and giant foxtail was not significantly different from the percentage recovered from corn, but the head capsule widths of larvae recovered from corn was significantly larger than these species. Dry weight of larvae recovered was not significantly different between plant species. The host recognition bioassay previously used with western corn rootworm larvae also worked with northern corn rootworm larvae. 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: We evaluated the suitability of three grassy weed species, large crabgrass, giant foxtail, barnyard grass, and a forage grass, tall fescue, along with maize, as hosts of the northern corn rootworm. Northern corn rootworm eggs were infested on potted greenhouse plants, and after hatch, larvae were recovered over time using Tullgren funnels. The percentage larvae recovered varied significantly between species at each sample date. The highest percentage larvae were recovered from barnyard grass, maize, and large crabgrass followed by giant foxtail with tall fescue having the lowest larval recovery. When sample dates were combined to test the main effect of species, there was no significant difference in the percent larvae recovered between maize, barnyard grass, large crabgrass or giant foxtail. The change in head capsule width (growth to new larval instars) also varied significantly between grass species on the second, third, and fourth sample date, but not the first. On the second sampling date, most of the larvae from maize were third instars, and their head capsule width was greater than the head capsule width of larvae recovered from any of the other species. Although the greatest percentage of larvae were recovered from barnyard grass, average head capsule width of larvae recovered from all sample dates indicated they were mostly second instars. Average larval weights were not impacted by the grassy weed species evaluated. In a laboratory experiment, we also studied the host-searching behavior of neonate larvae in which the path patterns were observed after contact and removal from the roots of different species. In this study, we included the above species, as well as side-oats grama, sorghum, and moistened filter paper which was used as a control. There was a significant difference in the area searched, number of turns, path crossings, and the velocity in the behavior of the northern corn rootworm neonates exposed to the different plant species and the control (moistened filter paper). The importance of the results in relation to resistance management is discussed.