SOIL-MOISTURE AND LARVAL WESTERN CORN-ROOTWORM INJURY - INFLUENCE ON GAS-EXCHANGE PARAMETERS IN CORN

The western corn rootworm (Diabrotica virgifera virgifera LeConte) is an economically important pest of corn (Zea mays L.) in North America, but little is known about the physiological responses of corn to larv al corn rootworm damage. This study was conducted to (i) characterize how larval corn rootworm feeding affects corn photosynthetic rate (P-s ), stomatal conductance (g(c)), and intercellular CO2 concentration (C -i) and (ii) determine the interactive effects of larval injury and so il moisture on P-s, g(c), and C-i. To address Objective 1, a greenhous e and a field experiment in randomized complete block design compared rootworm-infested vs. noninfested Pioneer hybrid 3377 corn. Larval fee ding had significant and transient effects on leaf P-s and g(c) (but n ot C-i) in both experiments. When the rootworm population was predomin ately second instar, leaf P-s and g(c) in infested corn were significa ntly less (P < 0.05) than in noninfested corn; at the end of the larva l period, P-s and g(c) were not significantly different among rootworm treatments. Two greenhouse experiments addressed Objective 2. A facto rial design with high and low moisture levels and rootworm-infested an d noninfested plants was used. In both experiments, soil moisture leve l interacted with larval injury to significantly (P < 0.05) affect lea f P-s and g(c) (but not C-i). Within 24 h after the two moisture regim es were established, P-s of the noninfested plants dramatically increa sed, while rates of rootworm-infested plants did not change in plants that received supplemental water. Over 5 d, P-s rose in rootworm-infes ted plants until rates equilibrated among rootworm treatments that wer e given supplemental water. These results suggest that irrigation of i nfested corn may not immediately reduce the stress caused by larval in jury. A combination of factors (e.g., water uptake reduction, hormone synthesis in roots) may be involved in the injury-plant response proce ss.