Tolerance Monitoring Of Chilo Suppressalis(Walker) To Cry1Ab And Cry1Ca And Synergistic Activity Of Two Toxins Combination

Chilo suppressalis is one of the most important rice pests. Transgene technology provides the new strategy to control them. But the potential resistance risk of C.suppressalis to Bt rice threatens its utilities. Therefore, it’s necessary to know the tolerant level of C. suppressalis in the field to Bt rice, and make the suitable management strategy to delay the development of the resistance on this basis. In this study, we monitor the tolerance of the C. suppressalis in the field to Bt toxin using F1/F2 screen and discriminating dose. The results will provide the evidence to take high dose/refuge strategy and the resistance development in the field. In addition, we study the toxicity of the two Bt toxins combination,and the results suggest that double-gene/polygene strategies play an important role of synergism activity and resistance management.1. Tolerance Monitoring of C. suppressalis to Bt toxins: we have monitored 420 isofemale lines for Cry1 Ca and 203 isofemale lines for Cry1 Ab in Xingan region,Guangxi Province during 2012-2014. At the same time, we have monitored 172 isofemale lines for Cry1 Ca and 74 isofemale lines for Cry1 Ab in Fuzhou region,Fujian Province during 2013-2014. But we have never found the tolerant individuals for Cry1 Ca and Cry1 Ab in Xingan region over 3 years. However, we have found only one tolerant individuals for Cry1 Ab in two years in Fuzhou region. The results demonstrated that the tolerant level of C. suppressalis to Cry1 Ab and Cry1 Ca was very low and the variation of tolerant level is not obvious. what’s more, Compared the relative average development rating(RADR) of C. supperssalis on Bt diet in F1 generation between Xingan and Fuzhou populations, we find that the development of tolerance to Bt toxins varied differently under the different selective pressure.2. Synergism activity of the Cry1 Ca and Cry1Ab: susceptible,Cry1Ab-resistant,Cry1Ca-resistant strains of C. suppressalis were used for insect bioassays using the mixture of Cry1 Ca and Cry1 Ab at different ratio. We found the synergism activity at all ratios for susceptible and Cry1 Ab selective strains. For the Cry1 Ca strain, not all the mixtures have synergism activity but some mixtures have antagonism activity.In summary, in this study, the tolerant monitoring of C. supperssalis to Bt toxins in the field demonstrated that the low tolerance level of field C. supperssalis population to Bt toxins can provide theoretical basis for the implementation of high dose/refuge strategy. While synergism activity of Bt mixtures provides scientific basis for the development of new Bt rice with two or more insect-resistant genes for delaying the development of insect resistance.