Controlled field infestations with western corn rootworm (Coleoptera : Chrysomelidae) eggs in Missouri: Effects of egg strains, infestation dates, and infestation levels on corn root damage

Western corn rootworm, Diabrotica virgifera virgifera LeConte, feeding dama ge to corn roots resulting from different combinations of rootworm strains, infestation times, and infestation levels was evaluated in two factorial e xperiments. Each experiment was set up in a randomized complete block desig n with four replications and was repeated over three Missouri environments (one environment included bath experiments). The combination of the two fac torial experiments evaluated three sources of the western corn rootworm egg s (a nondiapausing lab strain, a diapausing lab strain, and a field strain) , three infestation times (planting, 2-leaf stage, and 5-leaf stage), and t wo infestation levels (600 and 1200 eggs/30.5 cm) in a total of five enviro nments which spanned three different years. The damage caused by the diapau sing strain was not significantly different from damage caused by the field strain in any of the environments or the combined analysis. The nondiapaus ing strain caused significantly more damage than the diapausing strain or t he field strain in the 1995 environment, but caused significantly less dama ge than the field strain in the 1996 Hinkson Valley environment. The infest ation of 1200 viable eggs/30.5 cm caused significantly more damage than the infestation of 600 viable eggs/30.5 cm in one experiment, but not in the o ther. The planting-time infestation caused significantly more damage than i nfestation at the 2-leaf stage, and infestation at the 2-leaf stage caused significantly more damage than infestation at the 5-leaf stage.