Effects of transgenic cotton on cabbage looper, tobacco budworm, and beet armyworm (Lepidoptera: Noctuidae) larval mortality and development and foliage consumption in the laboratory

Tobacco budworm larvae, Heliothis virescens (F.), were highly susceptible to feeding on Bt leaves or flower buds with 100% and 96% mortality occurring within 4 days, respectively, compared to an average mortality of 95% for cabbage looper, Trichoplusia ni (Hubner), and 57% for beet armyworm, Spodoptera exigua (Hubner), after 8 days on Bt leaves and 47% and 37% mortality on flower buds for four days. Larval weights, used as a measure of growth, of cabbage looper and beet armyworm after 7, 10, or 14 days of feeding on Bt leaves were lower compared with those feeding on non-Bt cotton leaves. Beet armyworm, cabbage looper and tobacco budworm larvae consumed significantly less Bt leaf area per feeding day compared with DPL 5415. However, a leaf-age effect showed that both species also consumed less leaf tissue and weighed less on old (7(th) to 9(th) node) vs. new (15(th) to 17(th) node) leaves of both DPL 5415 and Bt cottons. Leaf-age effects on larval mortality and pupation were variable.