Date of this Version
Western corn rootworm, Diabrotica virgifera virgifera LeConte, overwintering egg survival was studied at 3 soil depths (7.5, 15, and 30 cm), 3 soil textures (silty clay loam, loam, and sandy loam), and 2 surface residue treatments (with and without surface cover) at an eastern Nebraska site in 1989-1990 and 1990-1991. At a western Nebraska site, egg survival was evaluated at 3 soil depths (7.5, 15, and 30 cm), 2 surface residue regimes (with and without surface cover) within a fine sandy loam soil in 1989-1990. Overall, egg survival was low (30.0%) and intermediate (41.0%) at the eastern and western sites, respectively in 1989-1990 and high (64.7%) at the eastern Nebraska site in 1990-1991. Egg survival was significantly influenced by surface residue and by depth in all soil textures at the eastern site during both seasons. Percentage survival of D. v. virgifera eggs was <5 and ≈ 15% in the bare surface treatment at the 7.5 and 15 cm depths, respectively in 1989-1990. In 1990-1991, the lowest survival occurred in the bare surface treatment at 7.5 cm. Egg survival was not influenced by the surface cover or sample date at the western site. Simple regression equations showed significant relationships of percentage of egg survival with minimum soil temperature and with negative degree-days (1989-1990 only) at the eastern site. In 1990-1991, ≈80 negative degreedays or a minimum temperature of ≈-7°C was needed to significantly decrease D. v. virgifera egg survival. Multiple regression improved the prediction and showed the importance of snowfall and snow cover at the western Nebraska site and in 1990-1991 at the eastern site.