Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Jerry B. Graves

Abstract

Topical bioassays were conducted in 1991 to develop dose-mortality lines for the LSU laboratory reference colony (LSU-LAB) and field-collected colonies of tobacco budworm, Heliothis virescens (F.), from Louisiana, Mississippi and Texas. Field-collected colonies exhibited resistance to cypermethrin (1-41x), profenofos and sulprofos (1-8x), methomyl (2-6x) and no resistance to endosulfan compared to the LSU-LAB colony. Diagnostic dose bioassays were developed to facilitate rapid testing of field-collected colonies for resistance to insecticides. These diagnostic dose bioassays were conducted in 1992 and 1993 on the LSU-LAB colony, a North Carolina laboratory reference colony and field-collected colonies from Louisiana, Oklahoma and Texas. Significant (P $\le$ 0.01) levels of resistance to cypermethrin, endosulfan, profenofos, methomyl and thiodicarb were exhibited by all field-collected colonies (except one colony to thiodicarb) compared to the two reference colonies. Piperonyl butoxide (PBO) synergist bioassays resulted in significant (P $\le$ 0.05) increases in mortality for ten of twenty colonies compared to cypermethrin alone, two of fourteen colonies compared to profenofos alone, three of eleven colonies compared to methomyl alone and two of seven colonies compared to thiodicarb alone. Field test data with cypermethrin and PBO combinations indicated significant (P $\le$ 0.05) reductions in bollworm (Helicoverpa zea (Boddie)) /tobacco budworm damage and numbers of live larvae were achieved with cypermethrin (0.09 kg (ai/ha)) + PBO (1.12 kg (ai/ha)) compared to cypermethrin (0.09 kg (ai/ha)) alone. Topical bioassays were conducted with the R. T. Gast Insect Rearing laboratory colony (GAST-LAB) and twenty-three field collections of boll weevils, Anthonomus grandis grandis Boheman, from eleven parishes in Louisiana. The order of toxicity of the insecticides tested against the GAST-LAB colony from most to least toxic was cyfluthrin $>$ zeta-cypermethrin $>$ fipronil (($\pm$)-5-amino-1(2,$6$ -dichloro-$\alpha,\alpha,\alpha$-trifluoro-p-tolyl)-$4$ -tri-fluoromethylsulfinylpyrazole-3-carbonitrile) $>$ deltamethrin $>$ azinphosmethyl $$ oxamyl $>$ endosulfan $>$ malathion. There was no conclusive evidence of resistance to any of the eleven insecticides bioassayed against field-collected boll weevils, although LD$\sb{50}$s for cypermethrin were highly variable. The LD$\sb{50}$ values for AC 303,630, deltamethrin, endosulfan, fipronil, oxamyl and zeta-cypermethrin serve as baseline data.

Pages

170

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