Progress 10/01/00 to 09/30/05
Outputs
A simulation model was modified to include single gene and dual gene Bt corn and cotton types and to include anternate crop hosts of Helicoverpa zea. In a simulated mixed ecosystem pyramided Bt corn and cotton and soybeans greatly slowed resistance development. The model also shows that resistance evolution to be greatly slowed by other non-Bt sources of susceptible moths (e.g. wild and non-Bt crop hosts)
Impacts
Data and modeling will help relegulators to adopt new IRM requirements for new transgenic insecticidal cotton and corn as they come to market. Growers will benefit from reduced refuges and less risk of resistance development to those crops.
Publications
- Kurtz, Ryan W., Fred Gould, J. R. Bradley, and John Van Duyn. 2006. Evaluating Bt IRM requirements in North Carolina through computer modling. 2006 Proceedings Beltwide Cotton Conferences. pp. 1484-1491. National Cotton Council, Memphis, TN.
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Progress 10/01/03 to 09/30/04
Outputs
The long term performance of Yieldgard CryIAb Bt corn in northeastern NC was studied to determine the frequency and magnitude of economically positive responses. Trials were begun in 1996 and continued at one or more sites through 2004, except for 2002. Each comparison involved near-isogenic hybrids, with or without the Mon-810 or Bt-11 gene event; tests were conducted at 19 locations in eight counties. In 49 individual paired comparisons the Bt partner failed to increase yield 22.4% of the time, increased yield below the break-even threshold($7.00)4.1% of the time, and was profitable 73.5% of the time. This distribution reflects the temporal occurrence of damaging populations of European corn borer and/or southern cornstalk borer in northeast NC. The overall average benefit was $18.21 per acre, estimated at a corn price of $2.50/bushel.
Impacts
Long-term, wide area studies result in data that best reflects technology performance in commercial agriculture within the same region. This study, on Lepidoptera resistant Bt corn, reflects a variable performance that is characteristic to many products sold to farmers. Measurements of this variability, and the distribution of that variability, provide a basis for decision, concerning the use of the studied technology. Data are used in educational programs. Corn farmers in northeastern NC can recognize that the use of Yieldgard Bt corn has a high probability of being profitable and controlling the risk due to insect damage.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
We sought to use Helicoverpa zea survival data from CryIAb, CryIIAb, CryIAb + CryIIAb, and non-Bt field corn genotypes to calculate replacement rates and to assign fitness values for nine H. zea resistant genotypes. Relative fitness values were used to set parameters of a population genetics model assessing resistance management approaches. Replacement rates (egg to adult) were as follows: non-Bt=22.72, cryIAb=0.496,cry2Ab=6.064, and dual-toxin=0.015. Using a relative fitness(RF) value of 1.0 for the non-Bt the RF value for H. zea on each Bt genotype was: CryIAb=0.0218, cry2Ab=0.2669, and dual-toxin=0.0007. Values were then translated to RF values for each of the possible nine H. zea Bt resistant genotypes, considering two independent genes and partial dominance. The fitness values indicate H. zea genotypes fitness to cryIAb and/or cryIIAb toxins when exposed to each seperate toxin, or both combined. Data were used to test resistance development to a pyramided
genotype vs. simultaneously deployed single toxin genotypes under differing refuge systems. With zero or 5% refuge fewer generations were needed for resistance with the pyramided genotype. The oposite situation was observed with refuge sizes of 20% and 50%.
Impacts
Studies on this toxin complex and H. zea improve the basic understanding of resistance evolution in agriculture. Parameters for models simulating the evolution of resistance to dual toxin Bt corn and Bt cotton, within relevant agroecosystems, will be more realistically derived from these data.
Publications
- Storer, N.P., S.L. Peck, F. Gould, J.W. Van Duyn, and G.G. Kennedy. 2003. Spatial processes in the evolution of resistance in Helicoverpa zea (Lepidoptera: Noctuidae) to Bt transgenic corn and cotton in a mixed agroecosystem: a biology-rich stochasic simulation model. J. Econ. Entomol. 96:156-172.
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Progress 10/01/01 to 09/30/02
Outputs
The second-year of a life-table study was conducted on corn earworm (Helicoverpa zea) growth and survival in non-Bt, cryIAb, cryIIAb, and cryIAb+cryIIAb corn. Eggs were counted daily from 7/29 to 8/16 and categorized as new, ringed, or dark. No sig. differences occurred initially but larvae caused silks to dry prematurely in non-Bt and sig. differences in eggs were noted thereafter. Larvae were sampled from 7/30 to 9/06 at ca. 3 day periods. L1 larvae were initially very high but dropped dramatically after the first week due to Bt toxin or cannibalism, in the non-Bt. Toxicity to caterpillars among Bt lines was cryIAb < cryIIAb < cryIAb+cryIIAb.Mortality was high in all Bt lines but was more or less prolonged according to genotype. Few larvae in the dual toxin survived past the L1 stage. Little moth production resulted from cryIAb and cryIIAb and none from the dual toxin line. Moth production from the non-Bt was estimated at ca. 24,000 / acre. Results from near-isoline
comparisons of cryIab corn (Yieldgard brand Mon810 and Bt11 events)vs. non-Bt over a seven year period (20 experiments and many individual genotypes) show an average 7.03 bu/acre increase(range -0.9 to 20 bu/ac/year)and a gross value of + $17.56 / acre. Benetits of Yieldgard fluctuated with the level of European corn borer (Ostrinia nubilalis) and southern cornstalk borer (Dietrea crambidoides)infestation intensity.
Impacts
Dual-toxin Bt corn demonstrated high effectiveness against corn earworm and showed an advantage for grower profits and for insect resistance management. This information will useful to EPA, companies, and corn farmers. Documentation of the long term yield increases with Yieldgard brand Bt corn will be used in education programs targeted to corn growers.
Publications
- No publications reported this period
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Progress 10/01/00 to 09/30/01
Outputs
Life table studies with Helicoverpa zea on cryIAb, cryIIAb, cryIAb+cryIIAb,and non-Bt corn were conducted. Eggs were observed ca. daily through the ovipositional period and no significant differences were found. Larvae within ears were scored 8 times on ca. 3 day intervals. Non-Bt and cryIAb genotypes frequently had significantly more larva than cryIIAb and cryIAb+cryIIAb; the mean number of larvae for the scoreing period also showed this relationship. Larval mortality was ranked as follows: cryIAb+cryIIAb>cryIIAb>cryIAb>non-Bt. The growth of surviving larvae showed a similar ranking although cryIAb and cryIIAb were statistically the same on all scoring dates. Mass collections of ears containing last instar larvae or prepupa were held in pupation chambers,over soil. Estimated pupa per acre were 84, 726, 912, and 7527 for cryIAb+cryIIAb, cryIIAb, cryIAb, and non-Bt, respectively. Pupa were held until moths eclosed. Estimated moths per acre were 57, 656, 757, and 6238
for cryIAb+cryIIAb, cryIIAb, cryIAb, and non-Bt, respectively. Data indicated that cryIAb+cryIIAb may be "high dose". Larvae collected from all Bt genotypes were placed into culture to develop resistant progenies to each of the three toxin types/combinations.
Impacts
The refuge size needed to abate resistance evolution in Helicoverpa zea to cryIAb+cryIIAb toxins is influenced by the numbers of corn earworms emerging from the genotype containing the toxin mix. Our data indicate over 99.9% reduction in moths in this genotype vs non-Bt. The required (for IRM) 500:1 selected:non-selected moths may be met with refuge sizes smaller than the current 50% in cotton belt states.
Publications
- Burd, A. D., J. R. Bradley, Jr., J. W. Van Duyn, F. Gould, and W. Moar. 2001. Estimated frequency of non-recessive Bt resistance genes in bollworm, Helicoverpa zea. Proc. Beltwide Cotton Conf. 820-822. Storer, Nicholas P., John W. Van Duyn, and George G. Kennedy. 2001. Life history traits of Helicoverpa zea (Lepidoptera:Noctuidae) on non-Bt and Bt transgenic corn hybreds in eastern North Carolina. J. Econ. Entomol. 94:1268-1279.
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Progress 10/01/99 to 09/30/00
Outputs
Growth and survival of Helicoverpa zea was studied in ear-stage corn. New transgenic single gene-events were inferior to commercial CryIAb corn, as was one double-gene event. However, one double-gene Bt corn showed significantly higher mortality and very low growth of H. zea under high infestation. Light-trapped H. zea moths for single-line egg collection. Larvae were exposed to surface treated Bt toxin. We found one of 583 screened larvae appeared to carry a major gene for resistance to CryIAc. Assuming four possible genomes per individual, the gene frequency for resistance was estimated at 0.00043. Other females appeared to have minor genes for CryIAc resistance or major genes with lower levels of dominance. Also found one of 646 screened larvae that appeared to carry a major gene for resistance to CryIIAa; the gene frequency was estimated at 0.00039. Other females seemed to carry minor resistance genes.
Impacts
Impacts from these studies include: (1) identification of high-dose hybrids that may reduce the rate of resistance development in corn earworm and (2) demonstration of high efficacy corn hybrids for use to manage ear feeding and stalk boring insect pests.
Publications
- Burd, A.D., J. Bradley, J. Van Duyn, and Fred Gould. 2000. Resistance of bollworm to CryIAc toxin (MUP). Proc. 2000 Beltwide Cotton Prod. Res. Conf., National Cotton Council, Memphis, TN. pp.923-925.
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Progress 10/01/98 to 09/30/99
Outputs
Two Bt corn tests were conducted. Stacked and single gene Bt corn hybrids were examined for corn earworm and European corn borer efficacy. Plots were artificially infested at silking with laboratory reared corn earworm neonates and scored at 10 and 20 days. Non-Bt corn showed 1.3 larvae/ear, single Bt gene showed very low survival (<5%), and stacked Bt gene hybrids were completely free of larvae. Also, no feral European corn borers were found in the stacked gene hybrids. The second test compared near-isogenic lines of single CryIAb gene (events Mon-810 and Bt-11) events versus non-Bt. Feral European corn borer and southern cornstalk borer populations were very high. All Mon-810 and Bt-11 hybrids showed very high reduction in both species at all plant sites. Yields were increased from 15 to 20 bu/ac, depending upon the hybrid pair.
Impacts
Impacts from these studies include: (1) identification of high-dose hybrids that may reduce the rate of resistance development in corn earworm and (2) demonstration of high efficacy corn hybrids for use to manage ear feeding and stalk boring insect pests.
Publications
- N. Storer, F. Gould, G. Kennedy, and J. Van Duyn. 1999. Ecology and biology of cotton bollworm in reference to modeling Bt resistance development in a Bt cotton/ Bt corn system. Proceedings of the Beltwide Cotton Conferences. National Cotton Council. Memphis, TN. Pp 949-951.
- N. Storer, F. Gould, G. Kennedy, S. Peck, and J. Van Duyn. 1999. Evolution of region-wide resistance in cotton bollworm to Bt cotton as influenced by Bt corn: Identification of key factors through computer simulation. Proceedings of the Beltwide Cotton Conferences. National Cotton Council. Memphis, TN. Pp 952-955.
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Progress 01/01/98 to 12/31/98
Outputs
Efforts in 1998 have focused on evaluation of survival and/or developmental biology of Ostrinia nubilalis, Diatraea crambidoides, and Helicoverpa zea in Bt and non-Bt corn. Also, resistance evolution in H. zea was studied in a wide-area simulated environment containing Bt corn and Bt cotton. Last, the relationship of Bt corn and mycotoxin contamination was evaluated. Bt transformation events Mon-810, Bt-11, E-176, and CBH-351 were tested. Mon-810, Bt-11 and CBH-351 showed high efficacy vs. O. nubilalis & D. crambidoides. Whorl stage corn of all gene events showed minimal survival of neonate H. zea in the greenhouse. Mon-810 and Bt-11 showed ca. 25% the production of pupae vs. non-Bt near isolines and larvae development was slowed by ca. 6 days. CBH-351 showed no effect on H. zea survival or development. Computer simulation of Bt resistance in H. zea shown the following factors to be relatively important to the rate of resistance evolution: initial frequency of
resistance gene, functional dominance of resistance gene, proportion of susceptible larvae surviving on Bt, total proportion of corn in a region, and proportion of farms adopting Bt technology. Fumonisin was reduced in 1997 grain samples; results from 1998 are not yet available.
Impacts
(N/A)
Publications
- ILSI Health and Environmental Sciences Institute (ILSI HESI). 1998. Evaluation of Insect Resistance Management in Bt Field Corn: A Science-Based Framework for Risk Assessment and Risk Management. Report of an Expert Panel. ILSI Press, Washington DC.
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