Document Type

Thesis - University Access Only

Award Date

1996

Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

Abstract

Laboratory and field evaluations were carried out during 1993 and 1994 to determine the effects of soil insecticide application rates on the biologies of northern and western com rootworms, Diabrotica barberi Smith and Lawrence, and Diabrotica virgifera virgifera LeConte, respectively. Insecticide treatments for both studies included labeled (IX) and reduced (0.5 and 0.75X) rates of terbufos, tefluthrin, and chlorethoxyfos. Field plots were established in dry land continuous com Zea mays L., fields during the 1993 and 1994 growing seasons near Sinai and Aurora (Brookings Co.) South Dakota, respectively to investigate the effects of these treatments on root protection sex and species emergence levels and temporal emergence patterns of these insects. Mild to moderate levels of rootworm feeding pressure existed in study sites as was evidenced by root injury ratings of 2.7 and 3.7 in control plots for 1993 and 1994, respectively. Analyses showed that reduced application rates of these compounds are not likely to cause significant reductions in root protection, increases in total emergence, or shifts in temporal emergence patterns, irrespective of sex or species. Contrasts revealed that all insecticides had significant impacts on each of these properties in comparison with untreated plots. Insecticide applications resulted in highly significant (P = 0.0001) levels of rootworm feeding injury suppression when compared with untreated plots. Additionally, terbufos treatment caused 47 and 52% reductions in total emergence of female D. barberi and male D. v. virgifera, respectively, and significant (P ~0.0236) reductions of female D. v. virgifera were observed following applications oftefluthrin and chlorethoxyfos. Although rate responses were not observed, emergence of female D. barberi from tefluthrin-treated soil in 1993 was delayed by an average of 9.9 d compared with that from untreated control plots. Terbufos, tefluthrin, and chlorethoxyfos applications also resulted in significant (P < 0.05) lags in the onset of D. v. virgifera emergence during 1994. Rates of emergence per unit time were significantly (P < 0.05) more gradual with all insecticides on female D. barberi, with terbufos and chlorethoxyfos on male and female D. v. virgifera, and with tefluthrin treatment on both sexes of D. barberi. However, application rates did not significantly affect any of these parameters. Field-collected beetles from emergence study plots were retained in laboratory rearing cages and allowed to mate. All successfully-mated, gravid females were then isolated to assess fecundity and egg viability. Analyses indicated a trend (P = 0.0779) in increased number of eggs per female in D. barberi that survived terbufos-treated soil, whereas significantly (P = 0.0323) fewer eggs per beetle were collected from D. v. virgifera that survived 1 Xapplications oftefluthrin than from those that emerged out of 0.5X-treated plots. This disparity amounted to a 12% reduction in fecundity. Overall, the results of this project indicated that 0.5 and 0.75X application rates of these organophosphate and pyrethroid insecticides will not likely result in major impacts on insecticide efficacy, temporal emergence patterns, or the reproductive capacity of D. barberi or D. v. virgifera in comparison with currently labeled rates.

Library of Congress Subject Headings

Northern corn rootworm -- Effect of insecticides on

Western corn rootworm -- Effects of insecticides on

Corn -- Diseases and pests -- Control.

Format

application/pdf

Number of Pages

106

Publisher

South Dakota State University

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Rights Statement

In Copyright