Effect of the pollen of transgenic rice line, TT9-3 with a fused cry1Ab/cry1Ac gene from Bacillus thuringiensis Berliner on non-target domestic silkworm, Bombyx mori Linnaeus (Lepidoptera: Bombyxidae)

Abstract

Some cry genes from Bacillus thuringiensis Berliner (Bt) have been transferred into rice plants for resistance to lepidopterans. The ecological risks of Bt rice, especially the non-target effects of Bt rice pollen on the domestic silkworm, Bombyx mori Linnaeus in mulberry-rice mixed cropping area should be clarified cautiously. In light of B. mori fully domesticated and not surviving independently in the field, a series of laboratory bioassays were conducted to evaluate the effect of the pollen from an indica transgenic rice line, TT9-3 with a fused cry1Ab/cry1Ac gene on B. mori based on the investigation of rice pollen deposition under normal field conditions and the quantitation of the fused insecticidal protein expression in the pollen. No significant adverse effects were observed on the survival, growth and development of B. mori young larvae, even after the neonates had been exposed to Bt pollen at the highest density of 3,395.0 grains/cm² for 48 h which the pollen density is far higher than the highest pollen density on mulberry leaf, 1,635.9 grains/cm², naturally occurred in the field. According to these results and considering the extensive biotic and non-biotic factors such as the type of Bt genes used and expressed in Bt rice line TT9-3 which are safe to B. mori, the relatively low exposure amount of insecticidal protein in the Bt pollen, and other conditions which influence the silkworm's exposure to Bt pollens, it suggests that the pollen from Bt rice line, TT9-3 poses little effect on silkworm rearing in natural settings.