Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2004
Publication Date: N/A
Interpretive Summary: The ability of insect pests to give their offspring traits to survive Bt proteins will affect how fast resistance will develop to transgenic crops expressing these proteins. Individual corn earworms differed in the ability of their offspring to grow on the Bt protein Cry1Ac. Males collected from the field also produced families with greater tolerance of Cry1Ac than males from a laboratory colony. The conclusion is that the genetic potential to better tolerate Cry1Ac is present within populations of H. zea. Further research will aid in determining the field conditions that will allow this variation to lead to resistant populations.
Technical Abstract: The corn earworm, Helicoverpa zea (Boddie), is more intrinsically tolerant of Cry1Ac than another major pest of cotton, tobacco budworm, Heliothis virescens F. As a consequence, it has been speculated that the inheritance of tolerance to Cry1Ac may differ in these species. The purpose of the work presented in this manuscript was to determine if heritable variation for tolerance of the Bt protein Cry1Ac was present in H. zea. Full-sib family analyses were used to determine if larval development, one component of tolerance to Cry1Ac, was heritable in a laboratory population of H. zea. Approximately 54% of the total phenotypic variation for development of larvae feeding on Cry1Ac diet was attributed to genetic variation. Follow-up tests found a significant relationship between the larval development of parents and their offspring. The most tolerant families produced offspring with larval weights an order of magnitude larger than the least tolerant families. Variation among families for larval development was also correlated with survivorship on greater concentrations of Cry1Ac diet. Families originating from field-collected males also exhibited significant heritable variation for larval development on Cry1Ac diet (approx. 63% of phenotypic variation attributed to genetic variation). On average, families originating from field-collected males produced larvae that developed more rapidly on Cry1Ac diet than families sired by males from the laboratory colony. The presented data show that family analyses offer a useful methodology to incorporate into research programs for the genetic monitoring of resistance to Bt proteins.