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Ibrahim Ali and R. G. Luttrell University of Arkansas, Fayetteville, AR Craig A . Abel

Monitoring Bt Susceptibilities in Helicoverpa zea and Heliothis virescens : Results of 2006 Studies. Ibrahim Ali and R. G. Luttrell University of Arkansas, Fayetteville, AR Craig A . Abel USDA-ARS, SIMRU, Stoneville, MS. Previous Studies (2002-2005).

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Ibrahim Ali and R. G. Luttrell University of Arkansas, Fayetteville, AR Craig A . Abel

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  1. Monitoring Bt Susceptibilities in Helicoverpa zea and Heliothis virescens: Results of 2006 Studies Ibrahim Ali and R. G. Luttrell University of Arkansas, Fayetteville, AR Craig A . Abel USDA-ARS, SIMRU, Stoneville, MS

  2. Previous Studies (2002-2005) Collected and reared ~ 400 heliothine colonies. ~200 colonies assayed with Cry1Ac, Cry2Ab and Vip3A insecticidal proteins. Developed benchmarks for Bt resistance monitoring on cotton. Ali et al. 2003 to 2006 Beltwide Cotton Proc. Ali et al. 2006, J. Econ. Entomol 99: 164-175

  3. 2006 Studies: Colony Information 111 colonies, Larvae = 93 , Eggs= 18

  4. 2006 Studies: Colony Information

  5. Bioassays All assays were diet-incorporated, 3-8 rep/dose, 48-128 larvae/rep

  6. Bioassays Mortality (Larvae those died at 7 days post-treatment). Stunting (Larvae failed to molt to 2nd instars). Regressions for LC50 (Mortality) and MIC50 (Mortality + stunting) were estimated.

  7. Dose-response of H. zea Exposed to Cry1Ac UALabZA H. zea colonies exposed to doses (ug/ml) of Cry1Ac For Cry1Ac, 32 field populations had significantly lower mortality than 99.9% LCL for UA susceptible laboratory colony at the highest dose (250 ug/ml).

  8. Dose-response of H. zea Exposed to Cry1Ac UALAbZA LC50s for 28 field populations > susceptible laboratory colony. LC50s for 8 field populations > 250 ug/ml. MIC50s for 8 field populations > susceptible laboratory colony, and MIC50s for field populations varied over 100-fold.

  9. Correlation of mortalities and regression estimates for H zea exposed to Cry1Ac LC50 estimates of H. zea were significantly correlated with mortalities at highest tested dose of Cry1Ac(r=0.463, N= 42, P= 0.0174). The correlation coefficient for MIC50s and mortality +stunting was 0.596 (N= 42, P < 0.0001).

  10. Dose-response of H. zea Exposed to Cry2Ab UALabZA For Cry2Ab, 26 populations had significantly lower mortality than that of susceptible laboratory colony at the highest tested dose of Cry2Ab (150 ug/ml).

  11. Dose-response of H. zea Exposed to Cry2Ab UALabZA LC50s for 20 field populations > susceptible laboratory colony. LC50s for 6 field populations > 150 ug/ml. MIC50s for 18 field populations > susceptible laboratory colony, and MIC50s for field populations varied 69-fold.

  12. Correlation of mortalities and regression estimates for H zea exposed to Cry2Ab LC50 estimates of H. zea were significantly correlated with mortalities at highest tested dose of Cry2Ab (r=0.705, N= 31, P <0001). The correlation coefficient for MIC50s and mortality +stunting was 0.697 (N= 31, P < 0.0001).

  13. Dose-response of H. virescens Exposed to Cry1Ac UALabVR LC50s for three field populations > UALabVR colony and varied 7-fold.MIC50s varied only two-fold across all colonies.

  14. Dose-response of H. virescens Exposed to Cry2Ab UALabVR Susceptibilities of all H. virescens populations exposed to Cry2Ab varied 2- to 3- fold.

  15. LC50s for H zea field populations exposed to Cry1Ac in assays against different generations in laboratory culture a a b LC50s of populations exposed to Cry1Ac tended to decrease in laboratory culture.

  16. LC50s for H zea field populations exposed to Cry2Ab in assays against different generations in laboratory culture LC50s of field populations exposed to Cry2Ab decreased in laboratory culture.

  17. Conclusion Susceptibility of field colonies of H. zea to Cry1Ac and Cry2Ab varied significantly compared to the UA susceptible laboratory H. zea colony. Considerable variability exists in H. zea field colonies exposed to Cry1Ac and Cry2Ab. Susceptibility of field colonies to Cry1Ac was reduced through laboratory colonization. LC50 and MIC50 estimates for H. zea for Cry1Ac and Cry2Ab were significantly correlated with mortalities and mortalities + stunting. Susceptibility of field colonies of H. virescens to Cry1Ac and Cry2Ab varied 2- to 3-fold compared to the UA susceptible laboratory H. virescens colony.

  18. Acknowledgement This research was supported by a cooperative agreement with the USDA-ARS Southern Insect Management Research Unit, Stoneville, MS. Supports from Monsanto Company and U.S. EPA are acknowledged. We thank students and employees of the University of Arkansas for their assistance with field collections, rearing of insects and assays.

  19. Acknowledgement We like to thank and acknowledge the following research collaborators for providing insects for these studies: J. R. Bradley, Astrid Groot, North Carolina State University, Raleigh, NC. Greg Payne, State University of West Georgia, Carrollton, GA. Bill Moar, Auburn University, AL. Carlos Blanco, USDA-ARS, SIMRU, Stoneville, MS. Roger Leonard, Louisiana State University, Winnsboro, LA.

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