| The striped stem borer, Chilo suppressalis (Walker) is an importmant rice pest, widely distributed in the main rice-growing areas of Asia. In recent years, the damage of C. suppressalis on rice has increased greatly. At present, chemical control is the major method for protection rice from C. suppressalis damage. Remarkably, the control efficacy of these pesticides such as Bisultap and Triazophos, has declined rapidly due to the evolution of resistance to pesticides in C. suppressalis. An attractive alternative strategy for control of C. suppressalis is to produce insecticidal proteins by introducing the corresponding insecticidal genes into rice. Presently, many rice varieties transformed with genes encoding various Bacillus thuringiensis (Bt) or other insecticidal protein genes have been developed and shown high resistance to one or more lepidopteran pests of rice in field. However, potential ecological risk of insect-resistant transgenic rice to environment has become a public concern. In this study, resistanct screen, fitness cost of selective strains, resistant forecasting and resistant reality heredity were studied to evaluate the resistant risk of C. suppressalis to Bt toxin, which will provide scientific basis for insect resistant management and sustainable utilities of Bt rice. The results were shown as follows.1. The tolerant strains of C. suppressalis to Cry1Ac and Cry1Ab were selected for 21 generations and the tolerant levels were increased to 8.42-fold to Cry1Ac and 7.66-fold to Cry1Ab. The analysis of resistant reality heredity showed that the resistant reality heredities (h2).of Cry1Ac and Cry1Ab selected populations were 0.018 and 0.065, respectively. Resistant forecasting demonstrated that it would pass through 58~133 and 14~33 generations for C. suppressalis developing 10-fold resistance to Cry1Ac and Cry1Ab, when selection pressure in field was 50~90%, respectively.2. A certain fitness costs occurred in Cry1Ac and Cry1Ab screen populations of C. suppressalis, which were shown that the developmental time of lavae in both tolerant strains was obviously delayed and larval survival rates and emergence rates in both selective strains were significantly lower than that in susceptible strains.3. Temperature effect on the development, survivorship, fecundity, and life table parameters of C. suppressalis reared on an artificial diet was studied at six constant temperatures of 19, 22, 25, 28, 31 and 34±0.5oC, in order to provide the model parameters for population dynamic and tolerant evolution forecasting model of C. suppressalis on Bt rice. Individuals could complete development under all tested temperatures. The required developmental time decreased as temperatures increased from 19oC to 31oC and the pattern fitted well with Lactin models. The developmental threshold temperatures for egg, larva, pupa, preoviposition and the whole generation were 13.18oC, 15.44oC, 10.85oC, 14.14oC and 14.52oC, respectively. The effective cumulative temperatures of those life stages were 63.63, 365.11, 125.23, 19.35 and 569.86 degree days, respectively. The highest generation survivorship (61.2%), fecundity (159.5 eggs/female) and population trend index (39.0) occurred at 28oC, with high mating rate (75.0%) and the average number of spermatophores of 1.6/female. Both low (19oC) and high temperatures (34oC) adversely affected C. suppressalis development. The effect of temperature on generation survivorship (S) and population trend index (I) could be described as S = -0.3058x2 + 19.263x - 243.85 (r=0.95) and I = -0.4332x2 + 24.288x - 303.38 (r= 0.99). The information provides a solid foundation for C. suppressalis population forecast and development of sustainable management tactics.
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