Document Type

Thesis - University Access Only

Award Date

1995

Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Billy W. Fuller

Abstract

The effect of terbufos, fonofos, chlorethoxyfos, and tefluthrin on the mortality and movement of third-instar Diabrotica virgifera virgifera obtained from field and laboratory populations was studied. Bioassays were conducted on diapausing and non-diapausing laboratory populations of D. virgifera virgifera, a population of D. virgifera virgifera collected from Brookings County fields which had experienced unsatisfactory rootworm control in 1989, and a population of D. barberi reared from eggs collected in Brookings County, South Dakota. Comparisons of LC50 and LC95 values indicate D. virgifera virgifera larvae are more tolerant to terbufos than D. barberi larvae. D. virgifera virgifera obtained from field populations also exhibit significantly (P < 0.05) higher LC95 values to terbufos than the non-diapausing laboratory population of D. virgifera virgifera. Larvae obtained from both diapausing and non-diapausing laboratory populations had significantly (P < 0. 05) lower LC95 values than field collected D. virgifera virgifera. Results indicate field D. virgifera virgifera larvae are more tolerant to terbufos and fonofos then laboratory populations at the LC95 level. However, LC95 values are well below insecticide concentrations which would be expected in soils treated at the industry recommended rate. The unsatisfactory control which occurred during 1989 in fields from which the wild D. virgifera virgifera population was isolated was not due to physiological or biochemical resistance. There was no significant difference (P > 0.05) found between populations to chlorethoxyfos or tefluthrin. Experiments which examined the effect of insecticide treated soil on the distribution of third-instar D. virgifera virgifera were conducted using larvae obtained from a diapausing laboratory population. Larvae introduced into one half of a test arena containing soil which contained no insecticide were less likely to be recovered in the other half if it contained soil treated with fonofos, terbufos, or chlorethoxyfos. A negative relationship was found between dose and percentage of larvae recovered from treated soil. Tefluthrin had no significant (P > 0.05) effect on the area larvae were recovered in. Tests were conducted in which third-instar D. virgifera virgifera larvae were allowed to move toward the base of a corn plant through soil which had been treated with increasing concentrations of insecticide. Terbufos, tefluthrin, and acetone only were used as treatments. Results showed that distribution of larvae differed significantly (P < 0.05) between treatments which contained acetone only and treatments which contained terbufos or tefluthrin. The differing distributions did not appear to be caused by increased mortality or preferential occupation of the peripheral roots. Larvae were more likely to be recovered away from the plant base which contained lower concentrations of insecticide than close to the plant base where soil contained a higher insecticide concentration. In treatments which contained acetone, only larvae were recovered with equal frequency in both zones, indicating insecticides were affecting larval behavior.

Library of Congress Subject Headings

Western corn rootworm -- Larvae -- Effect of insecticides on
Corn -- Diseases and pests -- Control

Format

application/pdf

Publisher

South Dakota State University

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Rights Statement

In Copyright