Master of Science (MS)
Evolution of resistance in target pest populations is a major threat to the sustainability of transgenic crops expressing Bacillus thuringiensis (Bt) proteins. Fall armyworm, Spodoptera frugiperda (J.E. Smith), is a cross-crop target pest of Bt corn, Bt cotton, and Bt soybean. This pest, thus far, is the only target pest species that has developed field resistance to Bt crops in multiple areas across countries. Cry2Ab2 is a common Bt protein expressed in transgenic corn and cotton targeting lepidopteran pests including S. frugiperda. The objective of this study was to characterize fitness costs and inheritance of Cry2Ab2 resistance in S. frugiperda. In the fitness cost test, performance of the Cry2Ab2-resistant, -susceptible, and two reciprocal F1 colonies of S. frugiperda was assayed on non-toxic diet and non-Bt corn leaf tissue. Biological parameters measured were 7-day larval weight, neonate-to-pupa development time, neonate-to-pupa survivorship, pupal weight, sex ratio, and egg production. In the inheritance study, larval mortalities of the resistant- and –susceptible parents, and eight other cross-strains were assayed using diet-incorporated and leaf tissue bioassays with Cry2Ab2. Maternal effects were examined by comparing the larval mortalities between the two F1 strains. Dominance levels of resistance were measured by comparing the larval mortalities of resistant, susceptible, and F1 heterozygous strains. Number of genes associated with the resistance was estimated by fitting the observed mortalities of F2 and backcross strains with the Mendelian monogenic inheritance model. There were no significant differences among the four insect strains for all the fitness parameters measured with few exceptions, suggesting that the resistance was not associated with fitness costs. The Cry2Ab2 resistance in S. frugiperda was likely inherited as a single, autosomal, recessive gene. Information generated from this study should be useful in assessing resistance risk and developing management strategies for the sustainable use of Bt crop technology.
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Acharya, Binod, "Fitness costs and inheritance of Bt Cry2Ab2 resistance in fall armyworm, Spodoptera frugiperda (J.E. Smith)" (2017). LSU Master's Theses. 4566.