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

The Chrysomelid beetle Diabrotica barberi Smith and Lawrence is an important insect pest of corn in the western Corn Belt. Populations can exhibit extended diapause in which some eggs overwinter in the soil more than one year. Extended diapause enables D. barberi to circumvent the rootworm management practice of crop rotation (i.e., annual corn/soybean rotation) and can lead to root injury in first-year corn. During the last decade, D. barberi densities have been increasing in northeastern Nebraska and some first-year corn injury has been reported. As part of an effort to more clearly understand the biology and pest potential of D. barberi in Nebraska a study is being conducted to measure the frequency of extended diapause in populations of D. barberi from eastern Nebraska. Adult D. barberi collections were made during late summer 2008 and 2009 from 8 sites each year. 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. The extended diapause trait was found to occur in all eastern Nebraska populations included in the study. 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 the eastern-most counties of Nebraska. The frequency of extended diapause was lower in sites found west of the north-south transect. Possible mechanisms and relevance to D. barberi management are discussed.