Two Years Before the Hatch: Rootworms Adapt to Crop Rotation

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Abstract
Despite the widespread recognition that corn rootworms (northern, Diabrotica barberi Smith and Lawrence; and western, D. virgifera virgifera LeConte) can be controlled by crop rotation, there has been a persistent but erratic pattern of casual observations of damage to corn by rootworms in fields where corn is rotated annually with a nonhost crop. These reports are mainly from the northern cornbelt, and when the species involved has been identified, it has always been D. barberi. We observed 2 years of diapause in nearly half the eggs from adults collected from fields in three areas where corn is rotated annually. By contrast, only about 9% of the eggs were in diapause for 2 years when obtained from adults collected where corn is planted without rotation. Observations in 1985 of rootworm damage to corn in fields where the annual rotation of corn with a nonhost crop was modified by the “Payment in Kind” program in 1983 are explained most easily as due to the existence of prolonged diapause in the eggs. It appears that some populations of the northern corn rootworm may have adapted to crop rotation. This may be a case of an insect evolving an adaptation to a cultural practice.

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