Selected Grassy Weeds as Alternate Hosts of Northern Corn Rootworm (Coleoptera: Chrysomelidae)

Abstract

We evaluated the suitability of three grassy weed species, large crabgrass (Digitaria sanquinalis L. Scop.), giant foxtail (Setaria faber Herrm.), and barnyardgrass (Echinochloa crus-galli L. Beauv.), and a forage grass, tall fescue (Festuca arundinacea Schreb.), along with maize (Zea mays L.), as hosts of the northern corn rootworm, Diabrotica barberi Smith & Lawrence. Potted greenhouse plants were infested with northern corn rootworm eggs, and after hatch, larvae were recovered over time by using Tullgren funnels. The percentage of larvae recovered varied significantly between species at each sample date. The highest percentage of larvae were recovered from barnyardgrass, maize, and large crabgrass followed by giant foxtail and tall fescue. When sample dates were combined to test the main effect of species, there was no significant difference in the percentage of larvae recovered between maize and three other species (barnyardgrass, large crabgrass, and giant foxtail). The change in head capsule width (growth to new 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 was recovered from barnyardgrass, larval development on this species was reduced, because 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 studied the host-searching behavior of neonate larvae, in which the movement patterns were traced after contact with and removal from the roots of different species. In this study, we included the above-mentioned species, side-oats grama (Bouteloua curtipendula Michx. Torr), sorghum (Sorghum bicolor L.), and moistened filter paper, which served as a control. There were significant differences in the area searched, number of turns, path crossings, and the average velocity of the northern corn rootworm neonate larvae exposed to the different plant species and the control. The importance of the results in relation to resistance management is discussed.