EUROPEAN CORN-BORER (LEPIDOPTERA, PYRALIDAE) TUNNELING AND DROUGHT STRESS - EFFECTS ON CORN YIELD

The effect of simultaneous stresses from European corn borer, Ostrinia nubilalis (Hubner), tunneling and drought stress on corn, Zea mays L., yield was evaluated in a 2-yr field study. Physiological yield losses (i.e., potential yield that was not produced) and potential harvest yield losses (i.e., yield loss from stalk breakage) were both evaluated. European corn borer larvae were manually infested in the plants at corn pollen shed. Physiological yield losses up to 59.1% occurred in plants grown with slight irrigation (5% of full irrigation amount) compared with fully irrigated plants. An infestation of five larvae per plant (corresponding to 3.25 cavities per plant) reduced the corn yield across the irrigation gradient by an average of 18.8 and 13.3% in 1987 and 1988, respectively, compared with undamaged plants. Under conditions of severe drought stress, the percentage yield loss per larva generally increased as the soil moisture level decreased. In 1987, plants grown in soils near the field capacity moisture level suffered a 3.1% loss per larva, compared with a 7.1% loss in plants grown in dry soils (slightly over the permanent wilting point). Yield losses from larval tunneling were primarily caused by a reduction in kernel size rather than a reduction in kernels per ear. Drought stress frequently reduced both kernels per ear and kernel density. In addition, European corn borer tunneling resulted in a 9.3% yield loss from unharvestable ears.