| Transgenic Bt cotton varieties have been commercialized in a large scale. In this study, transgenic cotton varieties (GK12, Xinmian33B, SGK321) and their corresponding conventional cotton controls (Simian3, Xinmian33and Shiyuan321) were used to determine Bt toxin content at different developmental stages and different parts of transgenic cotton. The effects of Aphis gossypii feeding in transgenic cotton on the growth, development, the reproduction, the predation functional responses and search effects of Chrysoperla sinica were evaluated. Transfer of Bt toxin protein among transgenic cotton-A. gossypii-honeydew and nature enemies was studied. The main results were as follows:1. Temporal and spatial variation of the Bt toxin protein content in transgenic cotton showed that Bt gene was expressed in all organs, and there were significant differences in different growth stages of functional leaves. The variation trend was that the Bt expression was high and then decreased, and rose up a little at last, and seedling stage> bud stage> flowering> boll opening period>boll stage; the temporal variation of the Bt toxin protein content of bud, flower, bell also had similar trends. The spatial dynamics of Bt toxin proteins in the same period were consistent. The Bt toxin protein content of functional leaves was highest, and it was more than flowers, buds and other reproductive organs. Different leaf positions had a direct impact on the protein content of the Bt toxin. Bt toxin protein were significantly different in the different floral organs, that is, petal> flower> ovary> bract, and the Bt toxin protein in the bracts was far below the petals and other floral organs. Bt toxin protein in GK12bracts was the lowest, only147.9ng/g; highest Bt toxin protein was detected in SGK321functional leaves,1630.1ng/g,11.0times as the minimum content. In natural environment, the insecticidal protein in Bt cotton degraded much rapidly in the initial period and then slowered, it reached76.78%,82.03%and84.26%in first month (2010.9～2010.10) respectively in GK12, Xinmian33B, SGK321, and undetectable in late May.2. Impact on the growth development and the reproduction of C. sinica feeding on A. gossypii in different varieties of cotton indicated that after preying on the A. gossypii on different varieties of cotton, the mortality rate, the emergence rate and cocoon developmental duration, cocoon weight and adult sex ratio of C. sinica in cotton varieties were almost no significant differences; only the mortality rate of the first generation of C. sinica larvae feeding on A. gossypii in SGK321was only8.89%, extremely lower than the control (40.0%). The mortality rate of the second generation was16.09%, significantly lower than the control (75.9%); and the emergence rate of the first and second generations of the C. sinica larvae feeding on the A. gossypii of SGK321was high,1.18and1.17times as the control. There was no significant difference among the treatments of C. sinica adult in preoviposition; The spawning period for C. sinica feeding on the A. gossypii of transgenic cotton were longer than the control; the oviposition duration of the first generation of C. sinica feeding on the A. gossypii in SGK321was up to33.01d, significantly longer than the control. The fecundity of C. sinica feeding on the A. gossypii in transgenic cotton was higher than the control. The fecundity of the first and second generation of the C. sinica feeding on the A. gossypii in33B and SGK321were significantly higher than control, and the fecundity of the first generation of C. sinica feeding on the A. gossypii in SGK321was up to882, which was extremely significantly higher than the control. There was no significant difference in egg hatchability between treatments. A series of studies showed that transgenic cotton had no adverse effects on the growth and reproduction of C. sinica. A. gossypii in transgenic cotton especially SGK321seems to have certain positive role in promoting the growth and development and reproduction of C. sinica.3. Predation functional response and searching rate of C. sinica larvae on A. gossypii were studied in laboratory. Predating numbers of C. sinica each instar larva increased with the density increase of A. gossypii in different cotton varieties. Most of the predating numbers of C. sinica feeding on A. gossypii in transgenic cotton were higher than those in conventional cotton. Predatory functional response of C. sinica each instar larva was consistent with Holling Ⅱ model pattern. According to the predatory functional response equation, we found that the daily maximum predation of C. sinica feeding on A. gossypii in transgenic cotton were higher than those in conventional cotton, while the treating time of C. sinica feeding on A. gossypii in transgenic cotton were less than those in conventional cotton. The daily maximum predation of C. sinica2nd and3rd instar larva feeding on A. gossypii in SGK321was29%and41%higher than the control. Search rate of C. sinica of each instar larva feeding on A. gossypii in transgenic cotton were higher than those in conventional cotton, and intraspecific interference of C. sinica of each instar larva feeding on A. gossypii in transgenic cotton were stronger than the control. Intensity of scrambling competition of C. sinica1st,2nd and3rd instar larva feeding on A. gossypii in GK12,33B, SGK321was29.6%,27.4%and69.6%, higher than those feeding on A. gossypii in Simian3. Therefore, the transgenic cotton had no harmful effects to the predation of C. sinica larva.4. In the food chain of transgenic cotton-A. gossypii-honeydew-Messor aciculatus and transgenic cotton-A. gossypii-C. sinica larva, we found there were a very high Bt toxin protein concentration of more than1000ng/g in transgenic cotton leaves, while a relatively low concentration in phloem sap compared with that in cotton leaves, which was only0.36% and0.37%at the seedling stage and the flowering stage, respectively. We also detected the Bt toxin protein of a small content in the cotton aphids fed with transgenic cottons, however, this content became a bit larger (1.16times) in A. gossypii feeding on transgenic cottons continuously for multi-generations, which indicats that with the increase of generation,Bt toxin protein accumulated in A. gossypii. There were also remarkable differences in the amount of honeydew secreted by A. gossypii fed with various kinds of transgenic cottons, in the conventional cotton field, the honeydew secreted was4.1g/d, which was2.28times that of SGK321.Bt toxin protein was detected in honeydew secreted by A. gossypii fed with transgenic cottons, but there was no obvious difference between different treatments. A small amount of Bt toxalbumin was also detected in M. aciculatus around the A. gossypii. There was no Bt toxin protein detected in C. sinica larvae of first or second generation feeding on A. gossypii in each transgenic cotton varieties. |
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