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Title: NUMBER OF POINT SOURCES OF WESTERN CORN ROOTWORM (COLEOPTERA: CHRYSOMELIDAE) EGGS IN ARTIFICIAL INFESTATIONS AFFECTS LARVAL ESTABLISHMENT AND PLANT DAMAGE

Author
item WILSON, TED - UNIVERSITY OF MISSOURI
item CLARK, THOMAS - UNIVERSITY OF MISSOURI
item Hibbard, Bruce

Submitted to: Journal of Kansas Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2005
Publication Date: 4/1/2006
Citation: Wilson, T.A., Clark, T.L., Hibbard, B.E. 2006. Number of point sources of western corn rootworm (Coleoptera: chrysomelidae) eggs in artificial infestations affects larval establishment and plant damage. Journal of Kansas Entomological Society. 79:119-128.

Interpretive Summary: The registration of transgenic corn with resistance to corn rootworm larval feeding offers a viable alternative to insecticides for managing the most economically important insect pests of corn. Maintaining susceptibility to transgenic crops (resistance management) is in the interest of growers, the Environmental Protection Agency, and industry, but requires an understanding of corn rootworm biology that does not currently exist. Mortality involved in host establishment is approximately ten fold higher in artificial infestations of the western corn rootworm in the field than in less compacted greenhouse soils. We hypothesized that the paths that western corn rootworm larvae use to find their host from an individual point source in the field may be limiting and become clogged or filled by early hatching larvae. To evaluate this 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). Damage from an infestation of 400 viable western corn rootworm eggs increased from one tenth of a node of roots pruned to approximately three fourths of a node pruned when the number of infestation points around the plant was increased from 1 to 16 at one of the two locations. However, there were no significant differences in adult emergence and only small differences in larval recovery from the differing number of point sources. The number of point sources around an individual corn plant may play a minor role in host establishment, but apparently does not play a major role. This information will be important to seed companies, the Environmental Protection Agency, and modelers in their attempts to develop resistance management plans for transgenic corn.

Technical Abstract: Density-independent mortality of larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte, during establishment on a corn plant is approximately ten fold higher in artificial infestations in the field as compared to artificial infestation in greenhouse 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 clogged or filled by early hatching larvae. To evaluate whether our hypothesis was correct, 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). Our hypothesis was partially supported by data from the current experiment. Damage 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. Damage from an infestation of 800 viable eggs increased 0.18 ± 0.11 to 0.56 ± 0.15 when the number of point sources increased from 2 to 16. 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 the Bradford Farm location. However, there were no significant differences in adult emergence. The number of point sources around an individual corn plant may play a role in host establishment, but apparently does not play a major role.