Studies On The Effects Of Transgenic Insect-Resistant Rice On The Field Composition Of Stem Borers And Its Mechanisms

Ecological safety of transgenic rice has been becoming a focus issue in the world. It's very important and necessary to evaluate the potential ecological safety systematically and scientifically before the commercialization of trangenic rice. In this paper, the effect of transgenic rice containing crylAc+CpTI toxin on field composition of striped stem borer (SSB), Chilo suppressalis, and pink stem borer (PSB) , Sesamia inferens were studied, and its possible mechanism was also preliminary studied. In addition, the susceptibility of two stem borers to Bt individual or combinations was also studied, and then help to guide the selection of effective toxins for breeding of transgenic rice. The main results were showed as follows.1 The results of field tests in both early and late rice indicated that the transgenic rice provided high levels of control against SSB and PSB. The number of SSB and PSB larvae on transgenic rice were significantly reduced compared with the non-transgenic control. Among the stem borers survived on transgenic rice field, the percentage of PSB increased significantly when compared with that on non-transgenic control.2 The laboratory bioassay results showed that the survival of SSB and PSB on transgenic rice was significantly lower than that on non-transgenic control. The toxic activity of transgenic rice to SSB and PSB declined significantly at the late growing stage. PSB on transgenic rice survived obviously better than SSB. As for SSB, no larvae could survive to the 5th day after infestation on transgenic rice. And some PSB larvae (2.3-7.3%) could survive at the 15^th day. Furthermore, there were a few PSB larvae (<1.6%) could pupate and some of them could emergence.3 Toxicity of several Bt protoxins against two stem borers (PSB and SSB) was compared by feeding neonate larvae on artificial diets containing Bt protoxins in the laboratory conditions. The results showed significant susceptibility differences between SSB and PSB to CrylAb, CrylAa, CrylBa, with the exception of the CrylCa and CrylAc, PSB was significantly low susceptible to the former three Bt protoxin compared with SSB. To evaluate possible interaction among these protoxin. toxicity assay was performed with mixtures of 2 Bt protoxins at 1:1 ratio. All the mixture protoxin showed significant synergistic toxicity activity against SSB. In contrast, only CrylAa-CrylAb mixture protoxin indicated moderated synergistic toxicity activity against PSB. In mortality-time response experiments, PSB showed more tolerance to CrylAb and CrylAc than SSB when treated with low or high concentration protoxin.4 The effects of the transgenic rice on ovipositional preference of PSB and the biology of Apanteles glomeratus, a parasitism for PSB, were investigated. It was observed that PSB did not obviously preferred transgenic rice to the control rice in ovipositional selection, and also, the transgenic rice showed no significant effect on the biological parameter of A. glomeratus species.5 Compared with PSB treated with the non-transgenic rice, the variation in biological traits of survived PSB was not observed when they were selected(1-2 generation)on transgenic rice in the field, including pupal weight, emergence rate, adult fecundity and the LC50 to CrylAc.To sum up, It's suggested that the varied susceptibility of two stem borer to transgenic rice rather than the ecological factor present here greatly contributes to a better understanding why the percentage of PSB increased obviously in transgenic rice field.