Field Termination of Egg Diapause in Diabrotica with New Evidence of Extended Diapause in D. barberi (Coleoptera: Chrysomelidae)

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Abstract
Eggs of the northern corn rootworm (NCR), Diabrotica barberi Smith and Lawrence, and the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, were placed in a soil pit outdoors at Brookings, S.D., in September (1982 for WCR, 1982 and 1983 for NCR) and removed from the pit at 20-day intervals through the winter to determine the pattern of termination of diapause under field conditions. Control eggs and eggs removed from the field were held in the laboratory at 25°C. With the WCR the percentage of egg hatch was the same whether the eggs had been incubated at 25°C in the laboratory or had been in the field for varying parts of the winter. A small percentage (<7%) of NCR eggs hatched without exposure to field conditions; hatch increased with increasing time in the field until midwinter, after which hatch was inconsistent. Some eggs underwent extended diapause. That is, following one winter in the field they did not hatch during 7 months at 25°C, but did hatch after a subsequent 4 months of chill. The occurrence of extended diapause has implications for the management of this pest.