Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Jerry B. Graves

Abstract

The pest status of the fall armyworm, Spodoptera frugiperda (J. E. Smith), including development and survival on conventional and transgenic Bacillus thuringiensis (Bt) cotton and host-strain influences, was examined in laboratory and field studies. Neonates (1st instars) were fed leaves from conventional (cv. DP 5415 and cv. DP 5690) and transgenic Bt (cv. NuCOTN 33$\rm\sp{B}$ and cv. NuCOTN 35$\rm\sp{B})$ cotton. There were no significant differences $(P>0.05)$ between cultivars in larval mortality and survival to the pupal and adult stages. However, times to pupation and adult eclosion were significantly longer $(P<0.05)$ for larvae fed transgenic Bt cotton compared to conventional cotton. In addition, larvae weighed significantly less $(P<0.05)$ when fed transgenic Bt cotton compared to conventional cotton. A study was conducted to determine when cotton bolls become tolerant to fall armyworm injury. Fifth instars were caged individually on bolls of various ages from conventional (cv. DP 5415) and transgenic Bt (cv. NuCOTN 33$\rm\sp{B})$ cotton to define the period of boll susceptibility to larval injury. For DP 5415 bolls, there was no significant linear relationship $(P>0.05)$ describing larval mortality or successful boll penetration as a function of boll age. Larvae were able to successfully penetrate ($>$60%) DP 5415 bolls throughout boll development. For NuCOTN 33$\rm\sp{B}$ bolls, there was a significant linear relationship $(P<0.05)$ describing larval mortality (increased as bolls developed) or successful boll penetration (decreased as bolls developed) as a function of boll age. Larvae were able to successfully penetrate ($>$40%) NuCOTN 33$\rm\sp{B}$ bolls at 350 heat-units. Studies were conducted to determine if there were differences in susceptibility between the two host-associated fall armyworm strains to conventional (cv. DP 5415 and cv. DP 5690) or transgenic Bt (cv. NuCOTN 33$\rm\sp{B}$ and cv. NuCOTN 35$\rm\sp{B})$ cotton or to selected insecticides. Fall armyworms collected from various forage grasses were consistently more susceptible to conventional cotton, transgenic Bt cotton, and selected insecticides than larvae collected from field corn. The utility of the sodium channel para locus to distinguish fall armyworm host-associated strains also was addressed. Genetic differentiation in the para locus was not correlated with host-associated strains. However, results suggest that this molecular marker is useful for distinguishing closely related Spodoptera spp.

ISBN

9780591905076

Pages

74

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