Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Jerry B. Graves

Abstract

Field cage studies were conducted to measure the effects of late season beet armyworm, Spodoptera exigua (Hubner), infestations (0, 1, 3, and 6 egg masses per 5.1 row m) on defoliation, fruit damage, and yield of cotton. Light penetration through the canopy was significantly higher in infested plots. Although a trend for increased numbers of damaged fruiting forms with increases in egg mass density was observed, there were no significant differences between infested and control plots. There were no significant differences in the cumulative number of shed fruiting forms or yield between infested and control plots. Field tests were conducted to evaluate the effectiveness of selected insecticides against native populations of beet armyworms. The experimental insecticides, chlorfenapyr, spinosad, and tebufenozide, provided satisfactory control (83-91%). Chlorpyrifos provided adequate (70-80%) control, while thiodicarb and Spod-X did not provide adequate control ($<$60%). Susceptibility of field-collected beet armyworm larvae to registered and experimental insecticides was evaluated in a diet overlay bioassay using 2-d old larvae and third instars (30-45 mg). Larvae were collected from cotton fields throughout the U.S. and from Rio Bravo, Mexico. Susceptibility of field strains was compared with a laboratory strain. In chlorpyrifos bioassays of 2-d old larvae, 7 of 11 field strains had significantly higher LC$\sb{50}$s, while in third instar bioassays, all field strains had significantly higher LC$\sb{50}$s. In thiodicarb bioassays, 3 of 10 and 5 of 8 field strains had significantly higher LC$\sb{50}$s in 2-d old and third instar bioassays, respectively. In bioassays of 2-d old larvae and third instars with chlorfenapyr, 1 of 9 and 5 of 8 field strains had significantly higher LC$\sb{50}$s. With spinosad, 3 of 10 field strains tested as 2-d old larvae had significantly lower LC$\sb{50}$s, while 1 of 7 strains tested as third instars had significantly higher LC$\sb{50}$s. With tebufenozide, 1 of 10 and 2 of 7 field strains had significantly higher LC$\sb{50}$s in 2-d old and third instar bioassays, respectively. Emamectin benzoate and methoxyfenozide were evaluated only in third instar bioassays, where 5 of 7 strains had significantly lower LC$\sb{50}$s and 1 of 7 strains had significantly higher LC$\sb{50}$s, respectively.

ISBN

9780591724028

Pages

97

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