The adult populations on and yield of plants infested with 600, 1200, and 2400 eggs of Diabrotica virgifera LeConte per plant were compared with check plants in 1972 and 1973. Results indicated that a corn plant has enough root system to sustain the rootworms which resulted from manual infestation of 600 to 1200 eggs/plant and still produce a near normal yield. Yield was significantly reduced only when the insects were so numerous and the damage to the corn root system so severe that the insects themselves suffered high mortality through competition for food. Results also showed that this critical population level was influenced by the amount of rainfall in the growing season. Thus, rainfall needs to be considered in assessing the economic threshold of this insect.
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Chiang et al. (1980) studied this question.