Frequency of extended diapause in Nebraska populations of the northern corn rootworm, Diabrotica barberi Smith and Lawrence (Coleoptera: Chrysomelidae)

This study was conducted to measure the frequency of extended diapause in populations of the northern corn rootworm, Diabrotica barberi Smith and Lawrence from eastern Nebraska.   Adult D. barberi collections were made during late summer 2008 and 2009 from eight sites each year (seven sites were consistent over years).  Eggs were obtained from 12-20 females per site and were held on moist soil under appropriate temperature profiles to facilitate egg survival, diapause development, and diapause termination within and among years.  Percentage egg hatch was recorded after the first and second year for the 2008 and 2009 collections.  Additional extended diapause expression was estimated for the 2008 and 2009 collections by counting remaining live eggs after the second year egg hatch was completed.   This data was also used to estimate each site’s maximum egg viability.  Results collectively indicate that the extended diapause trait occurred in all eastern Nebraska populations; however, significant variation in the frequency of extended diapause was observed within and among D. barberi populations.  Geographically, the highest incidence of extended diapause was found in a north-south transect in eastern counties of Nebraska that parallel the Missouri River.   In general, the frequency of extended diapause was lower in sites found west of the north-south transect.  This study contributes to the database needed to develop appropriate D. barberi management strategies in Nebraska.  Data can be used to pinpoint areas of Nebraska that may have the greatest risk of economic injury in first-year corn when D. barberi densities are high.