The Potential Impact Of Transgenic Bt Rice On Propylea Japonica Thunberg

ABSTRACT Use of insect-resistant genetically engineered (IRGE) crops is driving the new "green revolution" in pest control. Planting of IRGE crops can bring huge benefits to the farmers, while it may bring potential ecological risks to the environment. In particular, the potential effects of IRGE crops on non-target arthropods have been drawing much attention. A ladybird beetle, Propylea japonica (Thunberg) is a well-known predator in multiple crop systems. In addition, they are known to use plant pollen as a supplemental food source. Thus they will be exposed to insecticidal protein produced by IRGE crops by preying on pests or consuming pollen, once IRGE crops are commercially grown. Therefore, it is necessary to assess the potential effects of IRGE crops, such as Bt rice, on this species before being commercially planted.This research mainly studied on feeding methods and the effects of insecticical proteins on P. japonica. For the first time using a rape seed pollen incorporated insecticical compound fed P. japonica. Toxicity measurement results confirmed the impact on growth and development of P. japonica.1) Using the rape pollen could meet needs of the growth and development of P. japonica. This diet was found to be suitable for a dietary exposure assay for P. japonica.2) We established and validated a dietary exposure assay by using the protease inhibitor E-64as positive control. Dose-dependent responses were documented for all observed life-table parameters of P. japonica including survival, pupation and eclosion rates, development time and adult weight. Results suggested that the dietary assay could detect the effects of insecticidal compounds on the survival and development of P. japonica.3) Using the established dietary assay, we subsequently tested the toxicity of Cry1Ab, Cry1Ac, Cry1F, Cry1C and Cry2A proteins to P. japonica. The diet containing E-64was included as a positive control. P. japonica larvae were adversely affected when the diet contained E-64. Survival and development of P. japonica larvae were not adversely affected when the diet contained purified Cry1Ab, Cry1Ac, Cry1F, Cry2A at500μg/g diet and CrylC at200μg/g diet representing a worst-case exposure scenario.4) We conducted pollen-feeding assay to evaluate the potential toxicity of Bt rice pollen expressing Cry1C or Cry2A proteins to P. japonica, respectively. No negative effects were observed on test life-table parameters with an exception of a prolonged development time of P. japonica larvae. This effect may be caused by altered nutritrional ingredients of Bt rice pollen comparing to non-transfored control pollen, but not by Cry proteins contained in Bt rice pollen since it has been confirmed that Cry1C and Cry2A has no toxicity to this species in our dietary exposure assays with purified Cry proteins.5) The bioactivity and stability of the Cry proteins in the diets and Cry proteins uptake by the ladybird larvae were confirmed by bioassay with a Cry-sensitive insect species and by ELISA.In summary, the current study demonstrate that P. japonica is not sensitive to Cry1Ab, Cry1Ac, Cry1F, Cry1C and Cry2A, and planting Bt rice expressing Cry1C or Cry2A protein will not cause direct effects on P. japonica, although a little, but significant prolonged larval development time when they feed the Bt rice pollen.