1 Published by Oxford University Press on behalf of Entomological Society of America 2017. This work is written by (a) US Government employee(s) and is in the public domain in the US. Field and Forage Crops Response of Maize Hybrids With and Without Rootworm- and Drought-Tolerance to Rootworm Infestation Under Well-Watered and Drought Conditions M. A. B. Mahmoud, 1,2 R. E. Sharp, 1 M. J. Oliver, 1,3 D. L. Finke, 1 M. Bohn, 4 M. R. Ellersieck, 5 and B. E. Hibbard 1,3,6 1 Division of Plant Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, MO 65211, 2 Department of Entomology, Faculty of Science, South Valley University, Qena 83523, Egypt, 3 Plant Genetics Research Unit, USDA-ARS, 205 Curtis Hall, University of Missouri, Columbia, MO 65211, 4 Department of Crop Sciences, University of Illinois, Urbana, IL 61801, 5 Agriculture Experiment Station Statistician, University of Missouri, Columbia, MO 65211, and 6 Corresponding author, e-mail: Bruce.Hibbard@ars.usda.gov Subject Editor: Michael Brewer Received 14 February 2017; Editorial decision 15 October 2017 Abstract Anecdotal data in the past have suggested that the effect of the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), on maize yield is greater under drought and the effect of drought is greater under rootworm infestations, but no ield experiments have controlled both moisture and rootworm levels. Field studies were conducted in 2012, 2013, and 2014 with treatments in a factorial arrangement of western corn rootworm infestation levels, and maize hybrids (with and without tolerance to drought and rootworm feeding). The experiment was repeated under well-watered and drought conditions in adjacent plots. Leaf water potential and stomatal conductance data suggested signiicant plant stress was achieved in the drought plots toward the end of the season each year and maize hybrids only played a minor role. In particular, in 2012 and 2013 yield was dramatically lower for the drought experiment than for the well-watered experiment. However, the impacts of rootworm infestation level and maize hybrids on water potential, stomatal conductance, and yield were variable across years and between experiments. In fact, the only year that the main effect of rootworm infestation levels signiicantly impacted yield was in 2014, when an extremely high infestation level was added and this was only for the well-watered portion of the experiment. Overall, rootworm infestation level played a relatively minor role in maize productivity and it did not appear that soil moisture level inluenced that to a large degree. Key words: Diabrotica virgifera, yield, soil moisture, water potential Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), the western corn rootworm, is the most economically damaging insect pest of maize (Zea mays L.) in the United States. Eggs over- winter in the soil, and to survive, the newly hatched larvae must locate roots of host plants, including maize and a few other grasses (Clark and Hibbard 2004, Oyediran et al. 2004). Neonate larvae typically begin feeding on the irst host roots that they encounter (Clark et al. 2006). Larvae develop through three instars and during that time they tend to move to and feed on the succulent new growth of nodal root axes as they arise from the base of the stem (Strnad and Bergman 1987a, Schumann et al. 2013). Western corn rootworm larval feeding impacts maize yield in several ways. Larval feeding can interfere with the ability of the plants to take up water (Gavloski et al. 1992, Hou et al. 1997, Erb et al. 2009, 2011), thus resembling drought stress and limiting plant productivity. Heavy larval infestations can also cause ‘goose necking’ or lodging of maize because damage to ‘brace roots’ (nodal roots that develop aboveground) and damage to other nodal root axes erodes the structural support delivered by these roots. The decrease in stalk stability that causes lodging adds an additional yield loss component as a result of dificulties in mechanical harvesting (Spike and Tollefson 1988, 1989, 1991). When averaged over 19 location- years in Illinois, a 15% yield loss was associated with one full node of damage (Tinsley et al. 2013). Damaged maize roots are also more likely to be infected by root and stalk fungal diseases (Palmer and Kommedahl 1969, Kurtz et al. 2010). Finally, adult western corn rootworm also impact maize as they feed on leaves, pollen, and silks, and, if heavy feeding occurs prior to pollen shed, can cause ‘silk- clipping’, which reduces pollination and results in lightly illed ears (Culy et al. 1992). Journal of Economic Entomology, XX(X), 2017, 1–16 doi: 10.1093/jee/tox309 Research Article Downloaded from https://academic.oup.com/jee/advance-article-abstract/doi/10.1093/jee/tox309/4670582 by University of Missouri-Columbia user on 08 December 2017