ENVIRONMENTAL AND EDAPHIC EFFECTS ON WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) OVERWINTERING EGG SURVIVAL

Western corn rootworm, Diabrotica virgifera virgifera LeConte, overwin tering 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 surfac e residue treatments (with and without surface cover) at an eastern Ne braska site in 1989-1990 and 1990-1991. At a western Nebraska Site, eg g survival was evaluated at 3 soil depths (7.5, 15, and 30 cm), 2 surf ace residue regimes (with and without surface cover) within a fine san dy loam soil in 1989-1990. Overall, egg survival was low (30.0%) and i ntermediate (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 de pth in all soil textures at the eastern site during both seasons. Perc entage survival of D. v, virgifera eggs was < 5 and approximate to 15% in the bare surface treatment at the 7.5 and 15 cm depths, respective ly in 1989-1990. In 1990-1991, the lowest survival occurred in the bar e surface treatment at 7.5 cm. Egg survival was not influenced by the surface cover or sample date at the western site. Simple regression eq uations showed significant relationships of percentage of egg survival with minimum soil temperature and with negative degree-days (1989-199 0 only) at the eastern site. In 1990-1991, approximate to 80 negative degree-days or a minimum temperature of approximate to -7 degrees C wa s needed to significantly decrease D, v. virgifera egg survival. Multi ple regression improved the prediction and showed the importance of sn owfall and snow cover at the western Nebraska site and in 1990-1991 at the eastern site.