Development of Spodoptera exigua and Helicoverpa zea (Lepidoptera: Noctuidae) on transgenic cotton containing CrylAc insecticidal protein

The effects of transgenic Bacillus thuringiensis (Bt)-cotton on three instars of Spodoptera exigua (Hubner) and Helicoverpa tea (Boddie) were studied. First, third and fifth instars were fed field-collected Bt-cotton leaves for 1, 2, 3, 4 and 7 d or until pupation, and then transferred to artificial diet. Larval mortality at pupation, length of larval and pupal periods, pupal weights and survival time from hatch to adult were recorded for regular and Bt-cotton. Larval mortality at pupation in S, exigua fed Bt-cotton was low for all instars exposed and feeding periods on Bt-cotton. The mortality in H, tea was high for first and third instars and significantly increased with the increase in feeding period on Bt-cotton (P < 0.05). The length of larval period increased in both species when first and third instars but not fifth instars were fed Bt-cotton. In H. tea, the larval period increased when larvae were on Bt-cotton leaves for only 2 d. Pupal weight was reduced with an increase in feeding time on Bt-cotton in all three instars in both species. An increase in length of feeding time on Bt-cotton reduced survival to adults in both species on Bt-cotton in first and third instars but not in fifth instars. Survival to adults was much lower in H. zea than S. exigua for all instars exposed and feeding periods on Bt-cotton. These results demonstrate the large differences in effectiveness of Bt-cotton against lepidopteran cotton pests, as well as the adverse effects on larvae developing on Bt-cotton.