Number of Point Sources of Western Corn Rootworm (Coleoptera: Chrysomelidae) Eggs in Artificial Infestations Affects Larval Establishment and Plant Damage

Abstract Host establishment of larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte, on a corn plant is approximately ten fold higher in artificial infestations in the greenhouse compared to artificial infestation in field experiments. We hypothesized that the paths that western corn rootworm larvae use to find their host from an individual point source (location where agar containing eggs is injected into the soil) in artificial infestations in the field may be limited and become obstructed by early hatching larvae. To evaluate our hypothesis, we tested two infestation levels (400 or 800 eggs/plant) each with five infestation patterns (1, 2, 4, 8, or 16 infestation points around the plant). An effect of infestation pattern was observed. Root damage on the 0 to 3 scale from an infestation of 400 viable western corn rootworm eggs increased significantly from 0.12 ± 0.03 to 0.74 ± 0.23 when the number of infestation points around the plant was increased from 1 to 16 at one location. Root damage from an infestation of 800 viable eggs increased from 0.18 ± 0.11 to 0.56 ± 0.15 as the number of point sources increased from 2 to 16 at the same location. In addition, larval recovery increased significantly from an average of 1.67 ± 0.49 to 6.22 ± 0.83 when the number of point sources increased from 1 to 8 for 400 viable eggs at one of the locations. However, there were no significant differences in adult emergence. The number of point sources around an individual corn plant apparently affects host establishment in a minor way.