Risk Assessment Of Bt Rice Pollen On The Domestic Silkworm, Bombyx Mori (Lepidoptera: Bombyxidae) And Biological Study Of The Bt Strain Safe To The Silkworm

In this paper, the safety of transgenic Bacillus thuringiensis (Bt) rice pollen grains on the domestic silkworm, Bombyx mori Linnaeus (Lepidoptera: Bombyxidae) is systematically evaluated under both laboratory and field conditions, and some biological properties of a new Bt strain, being safe to the silkworm, are also studied. The results are shown as follows.1 Toxicity effects of Bt rice pollen grains on the domestic silkworm, Bombyx moriAn ELISA was employed to quantify levels of the Cry protein in pollen grains from transgenic Bt rice lines KMD1, KMD2, Huachi2000Bl, Huanchi2000B6 and TT9-3 using a kit purchased from EnviroLogix Inc. (Portland, USA). The expression level of the Bt insecticidal crystal protein was estimated up to about 0.01% of total soluble proteins in pollen grains of TT9-3, which was significantly lower than that in pollen grains of other tested lines. The susceptibilities of the silkworm larvae with different instars to purified CrylAb protein and pollen grains from Huachi2000B 1 and TT9-3 were respectively measured using the bioassay method. TT9-3 pollen grains were about 313.2 times less toxic to the first instar silkworm larvae than pollen grains from Huachi2000Bl. The first instar larvae were about 3.83 times more susceptible to Huachi2000Bl pollen grains by comparison with the third instar ones. The purified CrylAb protein acted higher toxic to the silkworm larvae, being over 1000 times more than pollen grains from different tested Bt rice lines.2 Biological effects of Bt rice pollen grains on the domestic silkworm, Bombyx moriThe silkworm larvae were continuously exposed to the mulberry leaves contaminated by pollen grains on from Bt rice line, Huachi2000Bl and its non-Bt parental control cultivar (Jiazao 935) at two concentrations of Dl (1311.4±161.8 grains/cm2) and D4 (24824.6±1895.1 grains/cm2), being equivalent to LC20 and LC50 values of Huachi2000Bl pollen grains against the first instar larvae for different exposure periods under laboratory conditions. The exposure periods included from the first to third instar, the third to fifth instar and whole larval stage of the silkworm larvae.Bt rice pollen, especially at the concentration of D4, resulted in significantly higher larval mortality, longer developmental time, less body weight gain of early instar larvae, lower pupation and emergence rate, and poorer cocoon quality. The impact of Bt pollen grains on early instar silkworm larvae was more significant, and its consequence could be extended to the adulthood. These results suggested that high concentration of Bt rice pollen grains have dramatically adverse effects on biological characteristics of the silkworm such as larval survival, growth and development, and cocoon traits under laboratory conditions.3 Behavioral effects of Bt rice pollen grains of the domestic silkworm, Bombyx moriChoice tests were conducted to determine the changes in feeding behavior of silkworm larvae to Bt rice pollen using the method of leaf discs. When presented with a choice of leaf discs without pollen and leaf discs with high amounts of pollen, more larvae were found on the discs without pollen. However, when presented with leaf discs without pollen and leaf discs with small amounts of pollen, more larvae were found on the leaves with pollen. Choices of different instars to the discs with Bt or non-5? pollen at low density were much different. More first instars were found on the discs with non-Bt pollen, while late instars were found more and more on the discs with Bt pollen. As for Bt rice pollen, early instar larvae tended to choose leaf discs with the lower density of pollen, and late instars tended to the higher density of pollen.4 Physiological effects of Bt rice pollen grains on the domestic silkworm, Bombyx moriThe silkworm larvae with the first instar had been treated respectively by pollen grains from Bt rice line, Huachi2000Bl and CrylAb protein until pupation, and the activities of some digestive enzymes in the larval midgut, including amylase, lipase, tr...