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Measurements were taken of Bt protein expressed in the leaves of transgenic cotton (Gos- sypium hirsutum) transformed with a synthesized Bt (Bacillus thuringiensis) cry1A gene and its persistent level in larval bodies and faeces of a non-targeted insect pest, beet armyworm (Spodoptera exigua). We performed enzyme linked immunosorbent assays (ELISA) and bioassays using neonate larvae of cot- ton bollworm (Helicoverpa armigera) to detect the insecticidal activity of residual Bt protein at the sec- ond trophic level. The results showed that Bt protein content in functional leaves was different at various developmental stages and was different among plants at the same stage. Even though Bt protein concentration in the larval bodies and faeces de- creased 97.5%―99% compared to that found in cotton leaves subsequently fed to beet armyworm larvae, it still had a lethal effect on neonate cotton bollworm larvae. Therefore, Bt protein present at the second trophic level had insecticidal activity. This result is important in understanding and predicting the effect of transgenic plants on nontarget organisms.
Measurements were taken of Bt protein expressed in the leaves of transgenic cotton (Gos-sypium hirsutum) transformed with a synthesized Bt (Bacillus thuringiensis) cry1A gene and its persistent level in larval bodies and faeces of a non-targeted insect pest, beet armyworm ( Spodoptera exigua). We performed enzyme linked immunosorbent assays (ELISA) and bioassays using neonate larvae of cot- ton bollworm (Helicoverpa armigera) to detect the insecticidal activity of residual Bt protein at the sec- ond trophic level. The results showed that Bt protein content in functional leaves was different at various developmental stages and was different among plants at the same stage. Even though Bt protein concentration in the larval bodies and faeces de-creased 97.5% -99% compared to that found in cotton leaves fed fed to beet armyworm larvae, it still had a lethal effect on neonate cotton bollworm larvae. Therefore, Bt protein present at the second trophic level had insecticidal activi ty. This result is important in understanding and predicting the effect of transgenic plants on nontarget organisms.