Frequency and distribution of extended diapause in Nebraska populations of Diabrotica barberi (Coleoptera: Chrysomelidae).

The frequency of extended diapause in populations of the northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), was measured in eastern Nebraska. Adult collections were made during late summer in 2008 and 2009 from eight sites each year (seven sites were consistent over years). Eggs were obtained from 12 to 20 females per site and were held on moist soil under appropriate temperature profiles to facilitate egg survival, diapause development, and diapause termination. 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. These data also were used to estimate each site's maximum egg viability. Results collectively indicate that the extended diapause trait was present in all eastern Nebraska populations; however, significant variation in the frequency of extended diapause was observed within and among D. barberi populations (first-year mean percentage egg hatch range: 2008 collections: 4.5-38.6%; 2009 collections: 10.7-42.5%). Geographically, the highest incidence of extended diapause was found along a north-south transect in eastern counties of Nebraska that parallels 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 knowledge base needed to develop appropriate D. barberi management strategies in Nebraska. These data can be used to pinpoint areas of Nebraska that may have the greatest risk of economic injury in first-year corn (Zea mays L.) when D. barberi densities are high.