Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Conservation tillage practices are gaining wider acceptance nationally as erosion problems intensify in many agricultural areas. The western (WCR), Diabrotica virgifera virgifera LeConte, and northern corn rootworms (NCR), D. barberi Smith and Lawrence, collectively represent the most serious insect threat to corn following corn production in the Midwest. The rootworm life cycle is intimately linked to the soil. It has been hypothesized that modifications of edaphic features created by different tillage practices would impact the population dynamics of the WCR and NCR. Research concerning the role of tillage systems on corn rootworm ecology was thus initiated. The influence of tillage practices on WCR and NCR ovipositional behavior and overwintering survival were examined. No egg-laying preference for a tillage treatment was evident for either rootworm species. The influence of tillage on overwintering survival varied according to year. Western corn rootworm and NCR egg populations declined significantly during the winter of 1983-84 in the Paraplow and moldboard plow treatments. Populations were not significantly reduced in any tillage operation the second winter;Absolute estimates of spring egg populations and emerging adult populations were made each year for both species across tillage systems. Tillage practices did not significantly affect WCR or NCR survival throughout the growing season of corn. Western corn rootworm survival was greater than that of the NCR;Linear regression equations are presented that describe cumulative emergence on Julian date. Western corn rootworm emergence was delayed in conservation tillage treatments. The rate of WCR emergence in conservation systems was greater, however, than in conventional tillage operations. The NCR was less responsive in its emergence pattern to the different tillage operations;Larval populations and root damage were lower than expected in the no-till treatment relative to other tillage practices based upon absolute estimates of WCR and NCR spring egg populations. The ratio of WCR to NCR eggs was shown to be an important factor in establishing larval populations and precipitating root damage. The NCR is less capable of causing root damage than is a comparable population of WCRs.



Digital Repository @ Iowa State University,

Copyright Owner

Michael Eugene Gray



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129 pages