Effects of elevated atmospheric CO 2 (double-ambient CO 2 ) on the growth and metabolism of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), fed on transgenic Bacillus thuringiensis (Berliner) (Bt) cotton [Cry1A(c)], grown in open-top chambers, were studied. Two levels of CO 2 (ambient and double-ambient) and two cotton cultivars (non-transgenic Simian-3 and transgenic GK-12) were deployed in a completely randomized design with four treatment combinations, and the cotton bollworm was reared on each treatment simultaneously. Plants of both cotton cultivars had lower nitrogen and higher total non-structural carbohydrates (TNC), TNC:Nitrogen ratio, condensed tannin, and gossypol under elevated CO 2 . Elevated CO 2 further resulted in a significant decrease in Bt toxin level in GK-12. The changes in chemical components in the host plants due to increased CO 2 significantly affected the growth parameters of H. armigera. Both transgenic Bt cotton and elevated CO 2 resulted in a reduced body mass, lower fecundity, decreased relative growth rate (RGR), and decreased mean relative growth rate in the bollworms. Larval life-span was significantly longer for H. armigera fed transgenic Bt cotton. Significantly reduced larval, pupal, and adult moth weights were observed in the bollworms fed elevated CO 2 -grown transgenic Bt cotton compared with those of bollworms reared on non-transgenic cotton, regardless of the CO 2 level. The efficiency of conversion of ingested food and of digested food of the bollworm were significantly reduced when fed transgenic Bt cotton, but there was no significant CO 2 or CO 2 × cotton cultivar interaction. Approximate digestibility of larvae reared on transgenic cotton grown in elevated CO 2 was higher compared to that of larvae fed non-transgenic cotton grown at ambient CO 2 . The damage inflicted by cotton bollworm on cotton, regardless of the presence or absence of insecticidal genes, is predicted to be more serious under elevated CO 2 conditions because of individual compensatory feeding on host plants caused by nitrogen deficiency.
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