Modeling And Simulation Of Resistance Evolution In Cotton Bollworm To Two Bt Toxin In Northen China

As the main pest of cotton in our country, cotton bollworm population has been significantlyinhibited since Bt cotton widely planted from1997in northern China. Bt cotton planted now is single geneplant(express Cry1Ac toxin only), while express Cry1Ac insecticidal protein highly and sustainably in thevarious vegetative organs that forces cotton bollworm accelerating resistance evolution under highselection pressure. Gene pyramid products (express two or more Bt toxin simultaneously) whether controlresistance of cotton bollworm effectively or not needs much more sufficient assessments in China, andusing computer model to simulate gene pyramid products control resistance is the necessary choice. Soaccording to ecological factors and environmental factors such as Bt crops distribution, meteorological data,crop planting area, modeling and simulation field resistance evolution levels of cotton bollworm in northChina. Modeling and simulate changes of frequency after planting gene pyramid crops and underconditions of no exist or exist cross resistance between Cry1Ac and Cry2Ab toxins, aimed at analysiswhether gene pyramid strategies can control resistance effectively. All of this will supply technical supportsfor forecasting evolution of field resistance and establishing valid and reasonable strategies for delayresistance of cotton bollworm.Model had the hypothesie that resistance of cotton bollworm to Cry1Ac and Cry2Ab allcontrolled by a single autosomal gene. The resistance is incomplete recessive. Model simulation had gotideal results until the degree of dominance to Cry1Ac was0.36and0.39to Cry2Ab, fitness cost ofresistance gene to Cry1Ac was0.19and0.05to Cry2Ab. Compared model output data and field monitoringdata in1997-2009, results showed25%cases were failed predictions (7out of28) and75%predictionswere undifferentiated.If only planting Cry1Ac cotton and no any other Bt crops, the overall resistance frequency ofcotton bollworm to Cry1Ac toxins will growth year by year in northern China. Frequency of resistance toCry1Ac will up to0.0160in2030, which is as high as dozens of times of initial frequency (0.0005) whilekeep the level of initial frequency of0.0005to Cry2Ab. Field resistance of cotton bollworm populationshad been monitored in Henan Xinxiang in2013. The average development level of all female families onnormal diet between5.43and7.56, mean was6.66. The average development level on Cry1Ac diet were between2.09and5.67, mean was3.72. According to the screening result, estimated the frequency ofresistance cotton bollworm populations in Xinxiang was0.003151, which still in the sensitive period.When the degree of dominance of cotton bollworm to Bt toxin was less than0.5, i.e. incompletedominance or recessive, frequency of resistance at low levels and rising slowly either planting Cry2Abcotton or double Bt cotton. If the resistance of cotton bollworm was dominant inheritance, frequency ofresistance will rise gradually with the increase of the degree of dominance. The higher degree of dominance,the greater frequence of resistance.Planting the proportion of25%,50%Cry2Ab cotton and50%,70%,100%double Bt cottonwhich expressed Cry1Ac and Cry2Ab simultaneously can effectively reduce the levels of resistance offrequency when cross resistance of cotton bollworm doesn’t exist between Cry1Ac and Cry2Ab toxins,while Cry2Ab corn and double Bt corn can’t delay the evolution of resistance. If there were cross resistanceexisted in proportion10%and25%, using Cry2Ab cotton and double Bt cotton could control the resistance,while could not if the ratio of cross resistance over50%, namely, using gene pyramid strategies can’tprevent and control cotton bollworm resistance.Although resistance of cotton bollworm to single gene Bt cotton didn’t occur obvisualy to far,after more than one continuous generation of screening, studies had showed cotton bollworm had thecapacity to produce resistance to Bt cotton. In the present mode of Bt cotton planting, with the developmentof the time one day resistance will produced. According to the model simulation results, gene pyramidstrategies could effectively delay and suppress resistance on the base of no cross resistance. Crops whichexpress two Bt toxin whether commercialized in China need more adequate assessment, and using acomputer model to simulate two or more Bt gene crops to manage resistance of cotton bollworm is a mustchoice.