Browsing by Author "Reay-Jones, Francis"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Extended Sentinel Monitoring of Helicoverpa zea Resistance to Cry and Vip3Aa Toxins in Bt Sweet Corn: Assessing Changes in Phenotypic and Allele Frequencies of Resistance
    Dively, Galen P.; Kuhar, Tom P.; Taylor, Sally V.; Doughty, Helene; Holmstrom, Kristian; Gilrein, Daniel O.; Nault, Brian A.; Ingerson-Mahar, Joseph; Huseth, Anders; Reisig, Dominic; Fleischer, Shelby; Owens, David; Tilmon, Kelley; Reay-Jones, Francis; Porter, Pat; Smith, Jocelyn; Saguez, Julien; Wells, Jason; Congdon, Caitlin; Byker, Holly; Jensen, Bryan; DiFonzo, Chris; Hutchison, William D.; Burkness, Eric; Wright, Robert; Crossley, Michael; Darby, Heather; Bilbo, Tom; Seiter, Nicholas; Krupke, Christian; Abel, Craig; Coates, Brad S.; McManus, Bradley; Fuller, Billy; Bradshaw, Jeffrey; Peterson, Julie A.; Buntin, David; Paula-Moraes, Silvana; Kesheimer, Katelyn; Crow, Whitney; Gore, Jeffrey; Huang, Fangneng; Ludwick, Dalton C.; Raudenbush, Amy; Jimenez, Sebastian; Carrière, Yves; Elkner, Timothy; Hamby, Kelly (MDPI, 2023-06-25)
    Transgenic corn and cotton that produce Cry and Vip3Aa toxins derived from Bacillus thuringiensis (Bt) are widely planted in the United States to control lepidopteran pests. The sustainability of these Bt crops is threatened because the corn earworm/bollworm, Helicoverpa zea (Boddie), is evolving a resistance to these toxins. Using Bt sweet corn as a sentinel plant to monitor the evolution of resistance, collaborators established 146 trials in twenty-five states and five Canadian provinces during 2020–2022. The study evaluated overall changes in the phenotypic frequency of resistance (the ratio of larval densities in Bt ears relative to densities in non-Bt ears) in H. zea populations and the range of resistance allele frequencies for Cry1Ab and Vip3Aa. The results revealed a widespread resistance to Cry1Ab, Cry2Ab2, and Cry1A.105 Cry toxins, with higher numbers of larvae surviving in Bt ears than in non-Bt ears at many trial locations. Depending on assumptions about the inheritance of resistance, allele frequencies for Cry1Ab ranged from 0.465 (dominant resistance) to 0.995 (recessive resistance). Although Vip3Aa provided high control efficacy against H. zea, the results show a notable increase in ear damage and a number of surviving older larvae, particularly at southern locations. Assuming recessive resistance, the estimated resistance allele frequencies for Vip3Aa ranged from 0.115 in the Gulf states to 0.032 at more northern locations. These findings indicate that better resistance management practices are urgently needed to sustain efficacy the of corn and cotton that produce Vip3Aa.
  • Thumbnail Image
    Magnitude and Extent of Helicoverpa zea Resistance Levels to Cry1Ac and Cry2Ab2 across the Southeastern USA
    Reisig, Dominic; Buntin, G. David; Greene, Jeremy K.; Paula-Moraes, Silvana V.; Reay-Jones, Francis; Roberts, Phillip; Smith, Ron; Taylor, Sally V. (MDPI, 2023-03-07)
    After resistance is first detected, continued resistance monitoring can inform decisions on how to effectively manage resistant populations. We monitored for resistance to Cry1Ac (2018 and 2019) and Cry2Ab2 (2019) from southeastern USA populations of Helicoverpa zea. We collected larvae from various plant hosts, sib-mated the adults, and tested neonates using diet-overlay bioassays and compared them to susceptible populations for resistance estimates. We also compared LC50 values with larval survival, weight and larval inhibition at the highest dose tested using regression, and found that LC50 values were negatively correlated with survival for both proteins. Finally, we compared resistance rations between Cry1Ac and Cry2Ab2 during 2019. Some populations were resistant to Cry1Ac, and most were resistant to CryAb2; Cry1Ac resistance ratios were lower than Cry2Ab2 during 2019. Survival was positively correlated with larval weight inhibition for Cry2Ab. This contrasts with other studies in both the mid-southern and southeastern USA, where resistance to Cry1Ac, Cry1A.105, and Cry2Ab2 increased over time and was found in a majority of populations. This indicates that cotton expressing Cry proteins in the southeastern USA was at variable risk for damage in this region.