Modelling adaptabiity of cotton bollworm, Helicoverpa armigera (Hubner) to Bt-cotton in India

摘要

A stochastic model 'Bt-Adapt' was developed to simulate the rate of resistance development of Helicoverpa armigera to Cry1Ac under Indian farming conditions. The model integrates genetic and ecological parameters of H. armigera in relation to its response to the Cry1Ac expressing Bacillus thuringiensis (Bt)-cotton. Simulation analysis showed that relative survival rate of the Cry1Ac-resistant homozygous (RR), heterozygous (RS) and homozygous susceptible (SS) H. armigera genotypes on Bt-cotton, was the most important factor influencing resistance development. In the order of significance, the other factors that had the greatest impact on resistance development were the relative proportion of area under Bt-cotton, dominance of the resistant allele and initial frequency of resistant alleles in field populations. The extent of population reduction in Bt-cotton and non-Bt crops due to pest control, was found to have a significant impact on the rate of resistance development. Simulation studies showed that cultivation of Bt-cotton in 10, 20, 30 and 40% of the total area under cotton, is likely to result in resistant allele frequency reaching 0.5, which would be adequate to cause crop failure, after 54, 25, 16 and 11 years respectively, if no pest control measures were adopted in both Bt-cotton and non-Bt crops. With a pest control efficacy of 0.9 in Bt-cotton and 0.5 in non-Bt crops, it would take 70 and 45 years for resistant allele frequency to reach 0.5 with the Bt-cotton area at 30 and 40% respectively. Based on the simulation analysis, resistance management strategies are proposed with emphasis on reducing populations of H. armigera that survive Bt-cotton and enhancement of area of alternate host crops that are as attractive as cotton to H. armigera, to be used as trap crop or intercrop refuges.