Abstract: Larvae of the domestic silkworm, Bombyx mori(Linnaeus) could be influenced by Cry protein expressed in genetically engineered maize by consuming maize pollen. Laboratory experiments were conducted to evaluate the potential effects of transgenic maize GAB-3 expressing Cry1Ab and Cry2Ab. The toxicity of six purified Cry proteins that have been used in transgenic maize to silkworm were tested using dietary exposure assays. When the concentration of GAB-3 pollen on the leaves of mulberry was about 50 grains·cm^-2, no significant effect was detected on the survival rate of the neonate larvae of silkworm. The neonate larvae of silkworm could not survive beyond 14 d when the GAB-3 pollen concentration was about 500 grains·cm^-2. No adverse effect on the larvae weight was detected when they were fed with 10 grains·cm^-2 GAB-3 pollen for 7 days. But when the feeding time was prolonged or the density of GAB-3 pollen was more than 50 grains·cm^-2, the larvae weight was significantly decreased compared with the control larvae. The weight of the larvae decreased when they were fed with GAB-3 pollen or the non-transgenic maize pollen for 14 days or more. There was no significant difference in pupation rate, cocoon weight, pupa weight, cocoon shell weight between larvae fed with GM corn pollen or the non-transgenic corn pollen. Both of transgenic and non-transgenic maize pollen prolonged the development time of the larvae. The LC₅₀ of GAB-3 pollen to the neonate larvae of silkworm was 261.18 grains·cm^-2. While the treating time was prolonged, the LC₅₀ value decreased. Six purified Cry proteins that have been used for plant transformation were tested using dietary exposure assays. The toxicities of the tested six Cry proteins to B. mori were in the order: Cry1C>Cry1Fa>Cry1B>Cry2A>Cry1Ab>Cry1Ac. Cry1Ab and Cry2A were low toxicity to B. mori and they were commonly used in transgenic maize which was approaching commercialization in China. As in actual conditions, maize pollen density consumed by B. mori was lower than in lab, suggesting that the risk of Bt maize pollen on silkworm was negligible.

Key words: transgenic maize GAB-3, Bt protein, Bombyx mori, lethal concentration 50(LC₅₀)