The western corn rootworm, Diabrotica virgifera virgifera LeConte can affect water relations and yield of its host, maize ( Zea mays L.), under normal soil moisture. Drought stress negatively affects plant growth and yield. Anecdotal data have suggested that the effect of western corn rootworm is greater under drought and the effect of drought is greater under rootworm infestations, but few experiments have controlled both moisture and rootworm levels. We hypothesized that if drought and rootworms both occur, there would be a negative synergistic effect on maize growth and yield. To test this hypothesis, a series of greenhouse and field experiments were performed. Greenhouse experiments tested only one maize line at three different moisture levels and three different western corn rootworm infestation levels. This was done not only with neonate larvae, but also second instar larvae and eggs in separate, full experiments. Overall, the greenhouse results indicated that under the conditions of these experiments, the effect of drought was greater than the effect of western corn rootworm and the interactions between soil moisture level in western corn rootworm infestation level did not affect plant traits such as water potential, stomatal conductance, shoot air-dried weight, and root air-dried weight in most of the trials. Rootworms did add some interesting complexity to the greenhouse experiment. For instance, plants without western corn rootworm were more stressed than the moderate western corn rootworm infestation for the drought treatments in the third greenhouse experiment. Drought also impacted western corn rootworm larvae in the same experiment, but only when the larvae were already stressed at the highest infestation level. Field studies also were conducted in 2012, 2013, and 2014 with treatments varying soil moisture levels, western corn rootworm infestation levels, and maize hybrids with and without tolerance to drought and rootworm pressure. In 2012 and 2013, western corn rootworm infestation significantly impacted yield, but its impact on yield was much less than the effect of drought. When under drought and rootworm pressure, the Bt+AQUAmax hybrid with tolerance to western corn rootworm and drought was generally higher yielding and significantly less water-stressed than other hybrids. Root damage ratings were not significantly impacted by drought or its interactions with western corn rootworm infestation. Both drought and western corn rootworm affected water potential, stomatal conductance, root complexity, and beetle emergence. The magnitude of the effect of drought versus western corn rootworm infestation level varied depending on the factor being evaluated, but in general drought had a greater effect on maize growth factors. We must reject our hypothesis that rootworms and drought have a negative synergistic effect on maize growth and yield under the conditions of our study.
|Advisor:||Hibbard, Bruce E., Sharp, Robert E.|
|Commitee:||Ellersieck, Mark R., Finke, Deborah L., Oliver, Melvin J.|
|School:||University of Missouri - Columbia|
|Department:||Plant, Insects and Microbial Science|
|School Location:||United States -- Missouri|
|Source:||DAI-B 78/03(E), Dissertation Abstracts International|
|Keywords:||Damage, Diabrotica virgifera, Drought, Maize, Soil moisture, Western corn rootworm, Yield, Zea mays|
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