Effects of insect-resistant transgenic Bt rice with a fused Cry1Ab+Cry1Ac gene on population dynamics of the stem borers,Chilo suppressalis and Sesamia inferens,occurring in paddyfield

The approval of transgenic Bacillus thuringiensis rice(ab.,Bt rice) with double-stacked traits(including a rice restorer line of cv.Bt Huahui-1 and a hybrid rice line of cv.Bt Shanyou-63,both expressing a fused Cry1Ab+Cry1Ac gene) by China′s Ministry of Agriculture(MOA) on 27 November 2009 was a momentous day for biotech crops worldwide.To date,some experiments have been carried out in labs or under controlled environmental conditions,which indicate that Bt rice can perform remarkably well against two targeted lepidopteran pests(e.g.,the stem borer,Chilo suppressalis,and leaf-folder,Cnaphalocrocis medinalis),and simultaneously offers: 1) the potential to generate economic benefits due to yield increases,and 2) overall decreases in insecticide use in China.In this study,the field experiments were conducted in order to examine the population dynamics and damage characteristics of two stem borers(i.e.,target pest,C.suppressalis and a sub-target pest,Sesamia inferens) feeding on the Bt rice with a fused Cry1Ab+Cry1Ac gene(cv.,Bt Huahui-1) and its parent line of nontransgenic rice(cv.,Minghui-63).The results indicate that no significant differences were found in the number of egg masses per 100 plants for C.suppressalis or S.inferens occurring on Bt rice in contrast to nontransgenic rice.In addition,no significant differences in egg mass densities between C.suppressalis and S.inferens were found when fed on nontransgenic rice,whereasas a significant increase in egg mass were observed for C.suppressalis relative to S.inferens fed on Bt rice.Compared with nontransgenic rice,Bt rice significantly reduced the population density(i.e.,individuals per 100 plants;84.9%—100%) of C.suppressalis larvae,while the transgenicity did not significantly influence the population abundance for S.inferens.Moreover,C.suppressalis had significantly higher larval abundances than S.inferens when they fed on nontransgenic rice,while no significant differences were observed when fed on Bt rice.Simultaneously,significantly lower percentages of dead heart or white head plants(30.8%—98.3%),and damaged plants(11.4%—96.6%) resulted from C.suppressalis,while no significant differences were detected in the damage percentages for S.inferens,as they fed on the Bt rice relative to the nontransgenic rice cultivar.Therefore,Bt rice appears to have a higher resistance to the targeted pest,C.suppressalis,while lower resistance was observed for the sub-target pest,S.inferens.Furthermore,significantly higher damage percentages were caused by C.suppressalis relative to S.inferens,regardless of the transgenicity of the rice cultivar.Thus,the stem borer,C.suppressalis,remains the key insect pest in the paddyfield.While it is presumed,owing to the significant inhibition of Bt rice on the occurrence of C.suppressalis relative to S.inferens under the commercialization usage of Bt rice,the inter-species competition and population succession may be occurring between the target and sub-target pests of stem borers.Furthermore,additional field research work needs to be conducted,especially during the rice growing season when high densities of C.suppressalis and S.inferens are both available on Bt rice to assess ecological risks of the inter-species competition and population successions between the target and sub-target insect pests.