Potential Risk Assessment Of Insect-risistance Transgenic Bt Riceon Main Nature Enemies Of Nilaparvata Lugens

Rice is one of the most important food crops in the world. The infection of insect pests causes great amount of yield losses annually. Insect-resistant transgenic rice developed by genetic engineering technology is an efficient tool for rice lepidopteran pest control. However, the ecological safety of insect-resistant transgenic rice is a hot topic concerned by the public and scientists. The evaluation of non-target effects of insect-resistant transgenic rice on the natural enemies of herbivores is an important part of the environmental risk assessment, and should be conducted before the commercialization of any novel transgenic rice. T1C-19 and T2A-1 are relatively newly developed transgenic Bt rice lines, expressing cry1 C and cry2 A respectively, driven by the maize ubiquitin promoter, and both of them exhibits high resistance against lepidopteran pests of rice. In the present study, the assessments of the ecological safety of these two rice lines on predator Cyrtorhinus lividipennis(Reuter)(Hemiptera: Miridae) and Hylyphantes graminicola(Sundevall)(Araneae: Linyphiidae), and transgenic cry2 A rice on egg parasitoid Anagrus nilaparvatae(Pang and Wang)(Hymenoptera: Mymanidae) of brown planthopper, Nilaparvata lugens(St?l)(Hemiptera: Delphacidae) were conducted based on rice-brown planthopper-enemy tritrophic bioassays, high dosage exposure of Bt proteins, and field investigations of population dynamics. The results are as follows: 1 The assessment of potential ecological risk of transgeice Bt rice on predator C. lividipennisThe brown planthopper, N. lugens, is a main non-target sap-sucking insect pest of Bt rice, and C. lividipennis is the major predator of the eggs and young nymphs of planthoppers. As C. lividipennis may expose to the Bt protein via N. lugens, it is therefore essential to assess the potential effects of transgenic cry1 C or cry2 A rice on this predator. In the present study, three experiments were conducted to evaluate the ecological risk of transgenic cry1 C or cry2 A rice to C. lividipennis:(1) a direct feeding experiment in which C. lividipennis was fed an artificial diet containing Cry1 C or Cry2 A at the dose of 10-time higher than that it may encounter in the realistic field condition;(2) a tritrophic experiment in which the Cry1 C or Cry2 A protein was delivered to C. lividipennis indirectly through prey eggs or nymphs;(3) a realistic field experiment in which the population dynamics of C. lividipennis were investigated using vacuum-suction. Both direct exposure to elevated doses of the Cry1 C or Cry2 A protein and prey-mediated exposure to realistic doses of the two proteins did not result in significant detrimental effects on the developmental time, survival, female ratio and body weight of C. lividipennis. No significant differences in population density and population dynamics were observed between C. lividipennis in both transgenic Bt rice and nontransgenic rice fields. It may be concluded that transgenic cry1 C or cry2 A rice had no detrimental effects on C. lividipennis. 2 The assessment of potential ecological risk of transgeice Bt rice on predator H. graminicolaThe spider H. graminicola is a generalist predator, and may be exposed to the insecticidal proteins expressed in Bt rice through ingestion of rice pests. Survival, developmental time, body weight and fecundity of the spider did not differ when fed on N. lugens reared either on transgenic Bt rice(T1C-19 or T2A-1) or nontransgenic rice based on a tritrophic bioassay. Similarly, the functional response of H. graminicola did not differ between Bt or non-Bt rice. Cry1 C or Cry2 A protein did not accumulate in this spider when the prey N. lugens fed on transgenic cry1 C or cry2 A rice. No significant differences in population density and population dynamics were observed between H. graminicola in transgenic Bt rice and nontransgenic rice fields during a three-year field investigation. The results indicate that the life-table parameters tested in the present study, population dynamics and density of H. graminicola were not affected by transgenic cry1 C or cry2 A rice. 3 The assessment of potential ecological risk of transgeice Bt rice on parasitoid A. nilaparvataeA. nilaparvatae, is an egg parasitoid of the rice planthopper, N. lugens. In the current study, a seven generation bioassay was used to test for host-mediated effects of transgenic cry2 A rice(T2A-1) on this parasitoid. When A. nilaparvatae parasitized the eggs of N. lugens reared on either Bt or non-Bt rice, there were no differences in survival, development time, longevity, sex ratio or fecundity over seven generations. In addition, direct exposure to a high dosage of Cry2 A had no adverse effects on the survival or fecundity of A. nilaparvatae adults. Cry2 A protein could not be detected in the eggs of N. lugens or in the adults of A. nilaparvatae parasitizing eggs of N. lugens feeding on Bt rice. These results indicate that A. nilaparvatae are not sensitive to Cry2 A protein at the tested concentration and there were no detrimental effects on any life-table parameters in our study.