Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

David Boethel


In laboratory bioassays, total mortality (neonate to pupation) among Bt-cotton varieties ranged from 13 to 89%; however, only cvs. CK 312/531, NuCOTN 33B, and PM 1220 RR/BG caused greater mortality than the soybean and meridic diet controls. Several Bt-cotton hosts increased larval developmental time, but none of the commercial Bt-cotton varieties (excluding CK 312/531) significantly affected adult longevity, generation time, doubling time, or intrinsic rate of increase (rm). Soybean looper larval and predator densities were monitored in soybean fields to determine the impact of Bt-cotton production on soybean looper seasonal abundance. Throughout the study, peak soybean looper larval densities were greater in soybean adjacent to cotton compared to isolated soybean fields. However, densities in soybean fields adjacent to non-Bt-cotton never exceeded those sampled in soybean adjacent to Bt-cotton. Results from this study support the rm results from the laboratory experiment and indicate that local mortality caused by Bt-cotton is not having a significant impact on soybean looper densities in soybean within cotton-soybean agroecosystems. Susceptibility to foliar Bt-insecticides was monitored in 5 states and Puerto Rico from 1998 to 1999 using discriminating concentration and concentration-mortality bioassays. Throughout the study, field-collected soybean looper populations were less susceptible to Condor XLRTM in cotton-soybean agroecosystems than in areas without cotton production. Additionally, susceptibility to Condor XLRTM significantly decreased each year. None of the soybean looper populations evaluated were susceptible enough to MVPIIRTM to develop concentration-mortality regressions. Field-collected populations and laboratory-susceptible populations did not differ significantly in susceptibility to Dipel ESRTM and Xentari DFRTM.