Submitted to: Journal of Entomological Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/18/2008
Publication Date: 7/15/2008
Citation: Zhu, Y., Liu, F., Xu, Z., Chang, J., Abel, C.A., Shen, J. 2008. F1 screening for resistance gene alleles to bt cotton in helicoverpa armigera: how to differentiate s and r genotypes. Journal of Entomological Science. 43(3): 311-319 Interpretive Summary: To successfully use the F1 screening method which detects rare Bt-resistance alleles in an insect population, an accurate standard for identifying F1 individuals carrying the alleles is needed. The F1 screening method relies on the availability in the laboratory of a Bt-resistant insect strain that is crossed with field-collected individuals and the resulting progeny are tested on Bt cotton tissue. This technique was used in a study to survey a field population of Helicoverpa armigera in China for the presence of Bt-resistant alleles. After feeding on Bt cotton tissue for 5 days, insect growth stage (instar) was not a reliable indicator of resistance or susceptibility to Bt. Larval survival and, more importantly, larval weights, were more useful for detecting the presence of Bt-resistance alleles. A larval body weight of = 0.6 mg was effectively used to separate potential resistant families. A corrected surviving rate of >21.3% of sibling-mated F2 progenies were used to verify the resistance.
Technical Abstract: The F1 screening method relies on the availability in the laboratory of an insecticide-resistant insect strain that is used to detect resistance alleles at the same loci in field populations. This technique was used in this study to survey a field population of Helicoverpa armigera for Bt-resistant allele frequency. After treating F1 progenies derived from more than 260 single mating lines with Bt cotton tissue, there was no clear separation of resistant genotypes from susceptible genotypes based on their surviving rates which demonstrated an evenly linier distribution. We further analyzed larval growth of F1 progenies and found a correlation between larval body weight and surviving rate. The maximal correlation was obtained when F1 larval body weight reached = 0.7 mg. To avoid underestimation, a body weight of = 0.6 mg was used first to separate potential positive lines (resistant genotype). After that, a corrected surviving rate of >21.3% (the minimal theoretical rate of >25% for F0 males to carry sr and rr genotypes) was used as the criterion to examine F2 progenies derived from single sib-mating of F1 adults and to verify if the potential positive lines carried resistant alleles.