Comparison of screening techniques for western corn rootworm (Coleoptera :Chrysomelidae) host-plant resistance

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is one o f the most economically important insect pests of corn, Zea mays L. Many di fferent techniques have been developed for western corn rootworm host-plant resistance screening, but little has been done to compare the reliability and repeatability of these techniques. Seventeen maize cultivars were evalu ated for field adult emergence, vertical pulling resistance, and field/gree nhouse root feeding damage to determine the optimal method or combination o f methods to more quickly reach the goal of corn rootworm resistance in cor n. A rootworm host-search behavior bioassay was also conducted. Rank correl ation of root damage field performance among the 17 cultivars was found bet ween locations in both 1996 and 1997. Greenhouse root damage experiments ge nerally did not correlate to each other or to field locations. There was no correlation in percentage reduction of pulling force in infested versus no ninfested rows between 1997 paired-row pulling trials to other experiments. There was no correlation of field root damage performance in 1996 or 1997 to the 3 bioassay parameters tested: area searched, distance traveled, or n umber of path crossovers. It appears that the rootworm host-search behavior bioassay will not be useful in differentiating hosts within a species, and greenhouse damage ratings are questionable when comparing germplasm with l imited resistance. Field damage ratings should be the primary test before r esistance claims are made.