Published in Agron. J. 96:818-824 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
PRODUCTION PAPERS
Performance of Bt Corn Hybrids, their Near Isolines, and Leading Corn Hybrids in Pennsylvania and Maryland
Bryan L. Dillehaya,
Gregory W. Roth*,a,
Dennis D. Calvinb,
Robert J. Kratochvilc,
Gretchen A. Kuldaud and
Jeffrey A. Hydee
a Dep. of Crop and Soil Sciences, The Pennsylvania State Univ., University Park, PA 16802
b Dep. of Entomology, The Pennsylvania State Univ., University Park, PA 16802
c Dep. of Natural Resource Sciences and Landscape Architecture, Univ. of Maryland, College Park, MD 20742
d Dep. of Plant Pathology, The Pennsylvania State Univ., University Park, PA 16802
e Dep. of Agricultural Economics and Rural Sociology, The Pennsylvania State Univ., University Park, PA 16802
* Corresponding author (gwr{at}psu.edu).
Received for publication September 23, 2003.
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ABSTRACT
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The European corn borer [Ostrinia nubilalis (Hübner)] is an important pest of field corn (Zea mays L.) in the northeastern USA. One option for reducing yield loss from European corn borer (ECB) is the use of transgenic corn hybrids containing a modified Bacillus thuringensis (Bt) gene. This study evaluated Bt hybrids, their near isolines, and leading non-Bt hybrids for grain yield, moisture, and test weight under natural infestations of ECB in 2000, 2001, and 2002 at four to six locations across Pennsylvania and Maryland each year. Averaged over all locations and years, Bt, isoline, and lead hybrids yielded 9.1, 8.6, and 8.5 Mg ha–1, respectively. Grain moisture content at harvest was 224, 216, and 214 g kg–1 and test weight was 705, 713, and 713 kg m–3 for Bt, isoline, and lead hybrids, respectively. Overall, Bt hybrids produced higher yields, but also had higher grain moisture content at harvest and lower test weight than isoline and lead hybrids. Yield and moisture content differences were correlated with ECB infestations, but test weight was not. Isoline and lead hybrid yields were reduced by 2.37 and 2.60% respectively, for each ECB tunnel. Precipitation had no consistent effect on Bt and non-Bt hybrid differences for yield, moisture, or test weight. Delayed planting dates were associated with higher ECB infestations. This may be beneficial in predicting sites that could benefit from Bt hybrids. In some environments in Pennsylvania and Maryland, Bt hybrids can result in significant yield advantages.
Abbreviations: Bt, Bacillus thuringensis • ECB, European corn borer
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INTRODUCTION
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THE EUROPEAN CORN BORER is one of the most significant insect pests of field corn in the northeastern USA. The ECB is a multivoltine insect that damages corn plants by feeding in one to three generations per year in areas of the Northeast. European corn borer damage has been estimated to reduce grain yields by an average of 5.48% per larvae for first generation populations and 2.77% per larvae for second generation populations (Bode and Calvin, 1990). In Pennsylvania and Maryland, 0.6 million ha of corn were grown for grain production during 2001 with output valued at $359 million (NASS, 2002). Field surveys conducted by members of the USDA NC-205 committee and Bode and Calvin (unpublished data, 1990) indicate that annual ECB infestations average 0.37 larvae plant–1 for first generation populations and 1.56 larvae plant–1 for second generation populations. Provided that similar infestations occur in the Northeast, this would have resulted in an estimated annual loss of $35 million due to ECB for Northeast corn producers in 2001.
Transgenic Bt corn hybrids were introduced in 1996 and effectively control ECB and eliminate yield losses when subjected to economic ECB infestations. The cost effectiveness of these hybrids in the Northeast is uncertain, however. The added cost of Bt hybrid corn seed may be justified in areas with a high probability for ECB infestation (Hyde et al., 1999a, 2003) and higher levels of damage per larva. Better information on ECB infestations and yield and quality of Bt corn grown in the Northeast would help producers make more informed decisions when selecting hybrids for corn production.
Singer et al. (2000) conducted a 4-yr study in New Jersey comparing ECB damage associated with manure or N fertilizer applications and found Bt corn hybrids yielded 8 to 18% greater than non-Bt hybrids in the manure treatments, however only 2 to 6% greater in the fertilizer treatments (Singer et al., 2000). Cox and Cherney (2001) concluded that Bt hybrids did not yield more than conventional non-Bt hybrids and were not recommended for New York producers. A 2-yr Wisconsin study found Bt hybrids yielded similarly to or greater than non-Bt hybrids under moderate to heavy ECB infestations and were similar in grain moisture content (Lauer and Wedberg, 1999). This study also demonstrated that in the absence of ECB, elite adapted non-Bt hybrids yielded greater than Bt hybrids, suggesting an initial yield lag associated with Bt hybrids. In Ohio, Eisley (2002) found yields of Bt and isoline hybrids to be similar during a 6-yr field study. An Ontario study (Baute et al., 2002) reported similar yields from Bt and non-Bt hybrids, but the authors suggested the use of Bt corn only under heavy ECB infestations (>6 cm tunnels plant–1) and high corn prices. In the Corn Belt, Graeber et al. (1999) found the yield, moisture, and test weight to be similar for Bt and isoline hybrids under relatively low natural ECB infestations. In artificially infested plots, however, grain yield of non-Bt hybrids was reduced by 6.6%
This study was designed to address three objectives: (i) to compare the performance of Bt corn hybrids relative to their nearest isoline and to leading (i.e., top selling) conventional hybrids; (ii) to evaluate the consistency of yield, moisture, and test weight relationships among Bt, isoline, and lead hybrids across various seed companies; and (iii) to determine if any site characteristics were related to ECB infestation and yield response to Bt corn. Hybrid performance was evaluated across numerous locations with different site characteristics across Pennsylvania and Maryland.
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MATERIALS AND METHODS
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Fifteen field experiments were conducted in 2000, 2001, and 2002 at various locations in Pennsylvania and Maryland as noted in Table 1. Experimental sites in Pennsylvania were located at Hershey (south central Pennsylvania), Landisville (southeastern Pennsylvania), Williamsport (central Pennsylvania), and York (southern Pennsylvania). Maryland sites were located at Clarksville (central Maryland), Keedysville (western Maryland), and Wye (eastern Maryland) on University of Maryland research farms. Growing degree days (GDDs) were calculated using the Modified 30/10 Cutoff Method originally described by Barger (1969) and accumulated from the date of planting to the harvest date.
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Table 1. Planting date, harvest date, soil type, precipitation and growing degree days (GDD: 30/10°C system) at the study locations during the 2000, 2001, and 2002 growing seasons.
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At each site, corn was grown following soybean [Glycine max (L.) Merr.] on well-drained soils (Table 1). The Pennsylvania locations were grown using no-till practices. The Maryland locations were disked, cultivated, and culti-packed before planting. Planting dates ranged from 19 April to 17 May and harvesting dates ranged from 10 September to 1 November.
Three hybrid types, a Bt hybrid, its nearest isoline, and a leading non-Bt hybrid, were solicited from five different seed companies for this study. Due to seed availability issues, some hybrids were changed between years. Hybrids (Table 2) varied in relative maturity ratings from 111 to 118 d, but most were in the 111 to 114 d range. All Bt hybrids contained the Cry1A(b) endotoxin for ECB protection, although Agway, DEKALB, Doebler's, and Pioneer Bt hybrids were incorporated with the MON810 event, and Syngenta Bt hybrids were the Bt11 event.
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Table 2. The Bt, isoline, and lead hybrids from five seed companies planted during the 2000, 2001, and 2002 growing seasons. The relative maturity rating for each hybrid is shown in parentheses.
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At each location, each hybrid was replicated four times in a randomized, complete block design. Individual plots consisted of four rows, spaced 76 cm apart and were 6.1 m long. Plots were thinned to a final population of 64000 plants ha–1 at about the V5 stage. Weed control and fertilizer applications were managed by the cooperators. All plots were treated with an insecticide, tefluthrin, in a T-band application at 0.13 kg ha–1 to control soil insects.
European corn borer infestation data were collected from each plot by dissecting 10 corn plants in rows three and four. Plant dissection and observation were performed at harvest using a knife to split the plants parallel with the stalk. Live ECB larvae, ECB tunnels, ear damage, ear shank damage, and stalk damage data were then observed and recorded.
Grain yield, moisture, and test weight data were collected from rows one and two from each plot using a Massey Ferguson 8XP (AGCO Corp., Duluth, GA) research plot combine in Maryland and an Almaco SP40 (Almaco, Nevada, IA) research plot combine in Pennsylvania. A HarvestMaster grain monitor (HarvestMaster, Logan, UT) on each combine was used to collect yield, moisture, and test weight data for each plot. All grain yield data were corrected to 155 g kg–1 moisture content for statistical analysis.
All data were analyzed with mixed (MIXED) and regression (REG) procedures using SAS (SAS Inst., 2001). A combined analysis of variance was performed using the PROC MIXED procedure, with block and location as random variables and company and hybrid type as fixed variables. The combined analyses for yield, moisture, and test weight indicated significant interactions between location and hybrid type as well as frequent interactions between location, company, and hybrid type. Because of those interactions, each location was analyzed separately using the PROC MIXED procedure with block as random and company and hybrid type as fixed variables. Means were separated using Tukey's studentized range honestly significant difference (HSD) test to determine significant differences among hybrids (Zar, 1999). Linear regression procedures were performed using PROC REG of SAS. Regression slopes were compared using the method proposed in Zar (1999), which involves the use of the Student's t method of testing for differences. Results were considered significant in all statistical calculations at the 
= 0.05 level unless noted otherwise.
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RESULTS AND DISCUSSION
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Weather conditions varied among locations of the experiment (Table 1). The GDD accumulations were adequate at each location to ensure crop maturity. During 2000, all of the locations received adequate precipitation to avoid drought stress. Moderate drought stress occurred at the Keedysville and York locations in 2001 and severe drought stress occurred at the Wye and Hershey locations in 2002. The Hershey 2002 location received 406 mm of precipitation, but the distribution was less than ideal, contributing to severe midseason drought stress.
Grain yields averaged over all hybrids ranged from 4.2 Mg ha–1 at Hershey in 2002 to 13.3 Mg ha–1 at Wye in 2001 and this variation was primarily a function of drought stress. When averaged across all locations and years, Bt hybrids produced higher yields (9.1 Mg ha–1) than isoline and lead hybrids (8.6 and 8.5 Mg ha–1 respectively), which had similar yields (Table 3). The Bt hybrid yield advantage of 5.5% over isoline and lead hybrids was consistent with the estimated 6.4% yield loss due to ECB predicted by Bode and Calvin (1990) and was also consistent with the yield responses reported by Graeber et al. (1999) and Lauer and Wedberg (1999). Lauer and Wedberg (1999) reported a yield lag associated with lower yielding isoline hybrids, but yields of isolines in this study were equivalent to the lead hybrids. Apparently, Bt genes are now being incorporated into elite hybrids as Lauer and Wedberg (1999) predicted.
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Table 3. Grain yield, moisture, and test weight of corn hybrids grown in Maryland and Pennsylvania during 2000, 2001, and 2002.
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When averaged over all companies, Bt hybrids produced higher yields than isoline hybrids at 5 of 15 locations with yield responses ranging from 0.6 to 1.5 Mg ha–1, with the Clarksville 2000 location having the largest yield response to Bt hybrids (Table 4). At the remaining 10 locations, Bt hybrid yields were similar to isoline yields. The Bt hybrids had higher yields than lead hybrids at 5 of 15 locations, ranging from 0.9 to 1.9 Mg ha–1 higher, and were similar at 9 of the remaining 10 locations (Table 4). Isoline and lead hybrid yields were similar at 12 of 15 locations. At sites where ECB tunneling was low, such as Wye 2001 and Wye 2002, there were no differences between yields of the three hybrid types.
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Table 4. Grain yield, moisture, test weight, ECB larvae per plant, and ECB tunnels per plant of corn hybrids averaged over five companies for each location during 2000, 2001, and 2002.
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A significant company and hybrid type interaction in the combined analysis for yield (P = 0.0129) indicated the yield response to Bt was variable across companies (Table 5). Significant yield differences between Bt hybrids and their isolines were not consistent across companies. For example, DEKALB brand Bt hybrids entered in this study had significantly higher yields than isoline hybrids at 6 of 15 locations, whereas yields of Pioneer brand Bt and isoline hybrids entered in this study were not significantly different at any location (Table 5). This was likely due to a combination of larger responses to Bt for some Bt/isoline pairs and reduced statistical power of the hybrid comparisons at individual locations. The Bt hybrids exhibited a similar trend in significant yield differences across companies with lead hybrids. Pioneer brand Bt and lead hybrid yields were similar at all but one location, whereas significant differences appeared more frequent with other companies. Isoline and lead hybrid yields were similar within companies at most locations; however, Syngenta isoline and lead hybrids differed significantly at 6 of 15 locations with the isoline yielding higher at five of those locations (Table 5). Across all environments, the only significant difference between isoline and lead hybrid ECB infestations occurred with the Syngenta hybrids, with the isoline having a higher infestation than the lead (1.89 and 1.48 ECB plant–1, respectively). It appears that hybrids may vary in their yield response to the Bt gene as a result of a combination of variable natural ECB resistance and tolerance differences as shown by Barry et al. (2000). Identification of lead or isoline hybrids with good non-Bt ECB resistance or tolerance would be useful for planting in refuge areas.
Averaged over all companies and locations, Bt hybrids had higher grain moisture (224 g kg–1) than isoline and lead hybrids (216 and 214 g kg–1) (Table 3). Catangui and Berg (2002) also reported higher grain moisture content at harvest with Bt hybrids. Grain moisture of Bt hybrids was significantly higher than isolines at 9 of 15 locations and ranged from 5 to 22 g kg–1 higher (Table 4). Grain moisture differences were rather consistent across companies with Bt hybrids having significantly higher moisture contents than isoline hybrids ranging from 4 to 6 of 15 locations for each company (data not shown). Higher grain moisture of Bt hybrids relative to isoline hybrids suggests that maturity ratings of Bt hybrids should be rated 1 to 2 d later than their isoline and many seed company catalogs now reflect these differences in maturity between Bt hybrids and their isolines.
The Bt hybrids had significantly lower test weights (705 kg m–3) than those of isoline and lead hybrids (713 and 713 kg m–3, respectively), which were similar. This is in contrast to the finding of Graeber et al. (1999), who showed that Bt hybrids had similar test weights to non-Bt hybrids. The lower test weight of Bt hybrids may have been related to the delayed maturity of these hybrids as indicated by the higher grain moisture. From a practical standpoint, the slight reduction in test weight of the Bt hybrid grain would have a minimal effect on the price received for the grain. Among locations, Bt hybrids had a significantly lower test weight than isoline hybrids at 5 of 15 locations ranging from 8 to 15 kg m–3 lighter, and were similar at the remaining 10 locations (Table 4). The Bt hybrids had significantly lower test weight than the lead hybrids at 7 of 15 locations, ranging from 8 to 42 kg m–3 lighter, and were similar at the remaining eight locations. Isoline and lead hybrids were generally similar in test weight over all locations. Consequently, Bt hybrids were lower or similar in test weight than non-Bt hybrids grown under similar growing conditions for each location.
Grain test weight differences were consistent across companies with Bt hybrids having significant differences in test weight from isoline hybrids ranging from 3 to 4 sites out of 15 locations for each company with the exception of Agway and Doebler's hybrids (data not shown). Agway Bt hybrids were significantly lower in test weight than isolines at 7 of 15 locations and Doebler's Bt hybrids were significantly lower in test weight than isolines at 8 of 15 locations. No consistent relationships between isoline and lead hybrid test weight were found.
When averaged across all locations and years, Bt hybrids varied significantly from isoline and lead hybrids in ECB infestation density as well as in ECB injury characteristics, whereas the isoline and lead hybrids were similar (Table 6). The ECB infestations were significantly lower in Bt hybrids (0.02 larvae plant–1 and 0.05 tunnels plant–1) than isoline and lead hybrids, which were similar (0.72 and 0.74 larvae plant–1 and 1.68 and 1.57 tunnels plant–1, respectively) (Table 5). Further, Bt hybrids had significantly less exterior ear injury, interior ear injury, ear shank injury, and stalk breakage than isoline and lead hybrids (Table 6). Isoline and lead hybrids exhibited similar ECB damage levels and appeared to have similar levels of natural ECB resistance.
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Table 6. European corn borer (ECB) population and injury observed on corn hybrids grown in Maryland and Pennsylvania during 2000, 2001, and 2002.
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At each location, ECB larvae per plant concentrations were found to be significantly different between Bt hybrids and non-Bt hybrids at 6 of 13 locations where they ranged from 0.52 to 1.86 larvae plant–1 (Table 4). At some locations, ECB larvae were not present during sampling; most likely because they had developed into adults by this time. Significant differences in ECB tunneling among Bt and non-Bt hybrids were found at 11 of 13 locations where they ranged from 0.79 to 4.05 tunnels plant–1. Averaged over all companies, isoline and lead hybrid ECB larvae and tunneling per plant were similar at all locations. A company and hybrid type interaction was nearly significant (P = 0.0654) for ECB tunneling and was similar to previous research by Barry et al. (2000), suggesting variable hybrid differences in resistance. No differences in infestation or injury existed among the Bt hybrids.
Linear regression relationships between the yield response to Bt (difference in Bt hybrid yield vs. non-Bt hybrid yield) and influential site characteristics such as ECB infestation, precipitation, and planting date were evaluated (Table 7) based upon previous research (Hyde et al., 1999b; Godfrey et al., 1991; Mason et al., 1996). The Bt hybrid yield response was analogous to the yield loss attributable to ECB reported in previous studies. Measured Bt yield advantage per tunnel (2.31 and 3.21 for isoline and lead) were somewhat similar to that estimated by the model of Bode and Calvin (1990), which was 2.77% loss per larva. One outlier existed in the data: the severely drought stressed Hershey 2002 site. At this site, other factors besides the Bt gene may have influenced the relative yield differences among hybrids. With Hershey 2002 removed, the relationship between the difference in Bt and lead hybrid yield and ECB tunnels was significant (Table 7), and the expected yield losses per borer (2.37 and 2.60% for isoline and lead) approached the estimated value of 2.77% proposed by Bode and Calvin (1990). The difference between the linear regression slopes of the isoline and lead hybrids was found to be insignificant, which suggests that under identical ECB infestations, isoline and lead hybrid yields would be reduced at the same proportional rate.
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Table 7. Regression equations, r2, and model significance values for the relationship between corn yield, moisture, and test weight of Bt and non-Bt hybrids as influenced by ECB infestation, precipitation, and planting date during 2000, 2001, and 2002. Moisture and test weight are also compared with Bt hybrid yield benefit (Bt hybrid yield–non-Bt hybrid yield).
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The relationship between precipitation or planting date and Bt yield response was not significant, although there was a trend for higher yields with Bt hybrids over isolines as planting dates were delayed (Table 7). Early planting dates are considered to be an effective means for avoiding ECB losses (Mason et al., 1996).
Precipitation and planting date may be more appropriate in predicting ECB infestations, which in turn can be used to predict Bt yield benefits. Precipitation was not found to be significantly related to ECB tunneling (Table 8). Planting date was a significant indicator of ECB tunneling at the = 0.10 level. As planting dates were delayed, ECB tunneling was increased as suggested by Mason et al. (1996). One site, Hershey 2001, had high infestation levels (3.74 and 4.05 tunnels plant–1 for isoline and lead, respectively) despite relatively early planting (27 April). This indicates that in some situations, other factors such as little surrounding corn production or localized weather conditions, may result in high infestations despite early planting. This study supports previous research by Pilcher and Rice (2001) in that yield advantages associated with planting date and Bt corn for ECB management are somewhat still uncertain.
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Table 8. Regression equations and r2 values for the relationship between ECB infestation and precipitation, and ECB infestation and planting date during 2000, 2001, and 2002.
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The relationship between grain moisture differences of Bt and non-Bt hybrids with ECB tunnels, precipitation, planting date, and Bt yield benefit were generally not significant. Grain moisture differences between Bt and non-Bt hybrids appear to be somewhat linearly related to ECB infestation; thus, the moisture content differences increased as ECB infestation increased (P = 0.12 and 0.09 for isoline and lead hybrids, respectively). For consistency, these data were also analyzed without Hershey 2002 and the resulting relationship significance only slightly changed (P = 0.04 and 0.11 for isoline and lead hybrids, respectively). Graeber et al. (1999) suggested that high levels of ECB damage caused earlier senescence that may explain the observed differences between grain moisture contents of Bt and isoline hybrids. Both precipitation and planting date were not related to the Bt hybrid grain moisture response. The grain moisture response to Bt hybrids was related to the Bt yield response for isolines (P = 0.03), but not for the lead hybrids (P = 0.27). Thus, the grain moisture response of Bt hybrids appeared to be associated with higher infestations and yield responsive sites.
The relationships between grain test weight differences of Bt and non-Bt hybrids with ECB tunnels, precipitation, planting date, and Bt yield benefit were also generally not significant (Table 7). Thus, the slight test weight reductions associated with the Bt hybrids did not occur as consistently at sites with high infestation levels as did the higher grain moisture levels.
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CONCLUSIONS
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Across numerous environments where ECB infestations varied considerably, Bt hybrids resulted in increased corn grain yields in Pennsylvania and Maryland. Yield response to Bt hybrids in this study averaged 5.5% but varied depending on company and location. Some Bt hybrids appeared to result in less yield improvement relative to isolines than others and that appeared to be the result of increased tolerance levels for the isolines. These hybrids may be well suited for Bt corn refuges. On average, isoline and lead hybrids performed similarly, suggesting isolines now have similar yield potential and ECB resistance as lead hybrids. Environments with higher ECB infestations tended to result in the largest yield advantages to Bt hybrids. Yield of isoline and lead hybrids were reduced similarly, approximately 2.37 and 2.60%, respectively, for each ECB tunnel. Delayed planting was associated with higher ECB levels, which matches known insect–host relationships. Yield advantages to Bt hybrids were not consistently related to seasonal precipitation. Overall, responsive environments were somewhat unpredictable.
On average, grain moisture of Bt hybrids was increased relative to isoline and lead hybrids and test weight was decreased. Moisture differences occurred mostly at sites with significant ECB infestation levels and varied some with hybrids.
In some environments of Pennsylvania and Maryland, Bt hybrids can result in significant yield advantages and thus can be a profitable management option. Responsive environments, based on our study and others, appear to be associated with late-planted, high-yielding sites with a history of ECB, but more research is needed to better define these environments.
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ACKNOWLEDGMENTS
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This work was funded by a USDA–CREES Northeast IPM grant (2001-34103-10552). The authors appreciate the assistance of Wayne Haas, John Shaffer, and John Ayers in planting and harvesting some of the research trials used for this study. The support of cooperating corn growers Richard Snyder, Norman Miller, and Ritchie Flinchbaugh for providing field sites for this research is also greatly appreciated.
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REFERENCES
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- Barger, G.L. 1969. Total growing degree days. In Weekly weather and crop bull. 56:18 U.S. Dep. of Commerce and USDA, Washington, DC.
- Barry, B.D., L.L. Darrah, D.L. Huckla, A.Q. Antonio, G.S. Smith, and M.H. O'Day. 2000. Performance of transgenic corn hybrids in Missouri for insect control and yield. J. Econ. Entomol. 93:993–999.[Medline]
- Baute, T.S., M.K. Sears, and A.W. Schaafsma. 2002. Use of transgenic Bacillus thuringiensis Berliner corn hybrids to determine the direct economic impact of the European corn borer (Lepidoptera: Crambidae) on field corn in eastern Canada. J. Econ. Entomol. 95:57–64.[Medline]
- Bode, W.M., and D.D. Calvin. 1990. Yield–loss relationships and economic injury levels for European corn borer (Lepidoptera: Pyralidae) populations infesting Pennsylvania field corn. J. Econ. Entomol. 83:1595–1603.
- Catangui, M.A., and R.K. Berg. 2002. Comparison of Bacillus thuringiensis corn hybrids and insecticide-treated isolines exposed to bivoltine European corn borer (Lepidoptera: Crambidae) in South Dakota. J. Econ. Entomol. 95:155–166.[Medline]
- Cox, W.J., and D.J.R. Cherney. 2001. Influence of brown midrib, leafy, and transgenic hybrids on corn forage production. Agron. J. 93:790–796.[Abstract/Free Full Text]
- Eisley, B. 2002. Evaluation of Bt corn hybrids and equivalent non-Bt corn hybrids for yield [Online]. Available at http://entomology.osu.edu/ag/reports/02ecb.pdf (accessed 18 Sept. 2003; verified 19 Feb. 2004). Ohio State Univ., Columbus, OH.
- Godfrey, L.D., T.O. Holtzer, S.M. Spomer, and J.M. Norman. 1991. European corn borer (Lepidotera: Pyralidae) tunneling and drought stress: Effects on corn yield. J. Econ. Entomol. 84:1850–1860.
- Graeber, J.V., E.D. Nafziger, and D.W. Mies. 1999. Evaluation of transgenic, Bt containing corn hybrids. J. Prod. Agric. 12:659–663.
- Hyde, J., M.A. Martin, P.V. Preckel, and C.R. Edwards. 1999a. The economics of Bt corn: Valuing protection from the European Corn Borer. Rev. Agric. Econ. 21:442–454.
- Hyde, J., M.A. Martin, P.V. Preckel, and C.R. Edwards. 1999b. The economics of Bt corn: Adoption implications. Publ. ID-219. Purdue Univ. Coop. Ext. Service, West Lafayette, IN.
- Hyde, J., M.A. Martin, P.V. Preckel, L.L. Buschman, C.R. Edwards, P.E. Sloderbeck, and R.A. Higgins. 2003. The value of Bt corn in southwest Kansas: A Monte Carlo simulation approach. J. Agric. Resour. Econ. 28:15–33.
- Lauer, J., and J. Wedberg. 1999. Grain yield of initial Bt corn hybrid introductions to farmers in the Northern Corn Belt. J. Prod. Agric. 12:373–376.
- Mason, C.E., M.E. Rice, D.D. Calvin, J.W. Van Duyn, W.B. Showers, W.D. Hutchison, J.F. Witkowski, R.A. Higgins, D.W. Onstad, and G.P. Dively. 1996. European corn borer: Ecology and management. NCR Publ. 327. Iowa State Univ., Ames, IA.
- National Agricultural Statistics Service. 2002. Crop production: Annual summary [Online]. Available at http://usda.mannlib.cornell.edu/reports/nassr/field/pcp-bban/ (accessed 18 Sept. 2003; verified 19 Feb. 2004). Cornell Univ., Ithaca, NY.
- Pilcher, C.D., and M.E. Rice. 2001. Effect of planting dates and Bacillus thuringiensis corn on the population dynamics of European corn borer (Lepidoptera: Crambidae). J. Econ. Entomol. 94:730–742.[Medline]
- SAS Institute. 2001. The SAS system for Windows. Release 8.2. SAS Inst., Cary NC.
- Singer, J.W., J.R. Heckman, J. Ingerson-Mahar, and M.L. Westendorf. 2000. Hybrid and nitrogen source affect yield and European corn borer damage. J. Sustain. Agric. 16:5–15.
- Zar, J.H. 1999. Biostatistical analysis. 4th ed. Prentice Hall, Upper Saddle River, NJ.
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TOP
ABSTRACT
INTRODUCTION
