Abstract Agromyzid leafminers are important pests on various crops, including cotton. In this study, we determined the effects of Bt cotton (Bollgard II and DP-488-BtRR), conventional non-Bt cotton, and a mixture of Bt cotton and non-Bt cotton leaves on feeding and oviposition behaviors and longevity of Liriomyza trifolii adults, and development and pupation of larvae in the laboratory. Our results show that in a no-choice test, L. trifolii adults fed, oviposited and pupated more on non-Bt cotton than on Bt cotton. The adults lived longer when feeding on non-Bt cotton than on Bt cotton. The adult emergence were not significantly different when feeding on Bt and non-Bt cottons. The results were similar to those in the choice test when the leafminers were offered a choice among 2 different Bt cotton leaf and a non-Bt cotton leaf. The adults like feeding non-Bt cotton the most, followed by Bollgard II cotton, and then DP-488-BtRR, the least, and the feeding punctures were 158.5, 76.5, and 46.65 on the three types of cotton leaves, respectively. Number of eggs oviposited on non-Bt, DP-488-BtRR and Bollgard II cotton was 6.7, 1.7 and 0.75 per leaf, respectively. We also investigated the occurrence and damage of L. trifolii on cottons in the field.