A study was conducted to evaluate a cotton cultivar and five cotton seed-lines for resistance to silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and resistance to cotton leaf crumple disease caused by cotton leaf crumple geminivirus. Texas 121 is a cotton cultivar accepted for commercial production in the Rio Grande Valley, Texas. Texas 121 has resistance through phenological asynchronization to silverleaf whitefly through early maturity. Five breeding-lines from USDA-ARS being selected for various desirable agronomic characteristics were also included for whitefly and virus disease resistance screening. Results showed that there were differences in whitefly infestation levels and virus disease symptoms among the cotton entries in this study. The cotton cultivar, Texas 121, had a lower seed cotton yield than other entries in the study.