Responses of transgenic maize hybrids to variant western corn rootworm larval injury

Abstract

In 2005 and 2006, transgenic insecticidal maize hybrids (YieldGard Rootworm, MON 863, Cry3Bb1, Vector ZMIR 13L) were evaluated for their ability to limit root injury caused by western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding. Hybrids in each year of the experiment were planted in plots that had been devoted to a trap crop (late-planted maize interplanted with pumpkins) the previous growing season. All maize hybrids were provided by Monsanto Company and the genetic backgrounds remain unknown to the investigators. In 2005, the experiment was conducted in Urbana, Illinois. Urbana is located in east central Illinois, an area of the state in which a variant of the western corn rootworm has overcome the pest management benefits of crop rotation. Variation in root injury was noted across the maize hybrids in 2005 and the level of pruning increased from 20 July to 9 August for most hybrids. In 2006, the experiment was conducted in two locations, Monmouth and Urbana, Illinois. Monmouth is located in north-western Illinois and is within an area of the state in which densities of the variant of the western corn rootworm are lower than in east-central Illinois. In 2006, variation in root protection was again observed across the maize hybrids. Root injury differences among the hybrids were more prominent at the Urbana site. Similar to the previous year, root injury increased from the third week in July to the first week of August at both locations with this increase most noticeable at the Urbana location. We hypothesize that the variant western corn rootworm may be able to inflict more root injury to these transgenic insecticidal maize hybrids than the non-variant population of this species.

Field-evolved resistance to Bt maize by western corn rootworm: Predictions from the laboratory and effects in the field

“…Under higher levels of rootworm abundance, where the untreated control displayed injury of 1.5 nodes to greater than two nodes of injury, Cry3Bb1 maize always had less than 0.75 nodes of root injury (Ma et al, 2009). In a large-scale study conducted by Gray et al (2007), eight commercialized hybrids were evaluated in three separate studies. In each study, injury to the experimental control of non-Bt maize was at least 2.0 nodes and as high as 2.74 nodes.…”

Western corn rootworm and Bt maize

“…This level of injury is higher than other published accounts of injury for commercialized Cry3Bb1 maize hybrids. [55][56][57] Averaging across several studies, Dun et al 58 found a 17.9% reduction in yield for each node of roots lost to feeding by western corn rootworm, indicating that in seven of the fields visited in 2010 farmers may suffer substantial reductions in yield.…”

Impact of MON863 Transgenic Roots Is Equivalent on Western Corn Rootworm Larvae for a Wide Range of Maize Phenologies

“…Higher damage was particularly found in roots dug in early August compared with roots dug 3 wk earlier in midJuly, a more traditional time to evaluate corn rootworm damage (Gray and Steffey 2005). Gray et al (2007) reported that the average damage rating (Oleson et al 2005) of the eight commercial YieldGard Rootworm hybrids increased from an average rating of 0.17 on 24 July to 0.40 on 8 August 2006 in Monmouth, Mention of trade names or commercial products in this publication is solely for the purpose of providing speciÞc information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. IL, and from 0.31 on 20 July to 0.80 on 7 August 2006 in Urbana, IL.…”