An experimental isoline of field corn containing the gene for expression of the delta endotoxin of Bacillus thuringiensis was evaluated for its effects on a natural infestation of European corn borer in a single replication. Mature corn stalks that contain the Bt gene had much reduced ECB stalk tunneling compared to the isoline that did not contain the Bt gene. Yield samples revealed that the Bt corn had a numerically higher but statistically insignificant yield increase compared to the non- Bt corn. While the yield increase was not statistically significant at the 95% confidence level, yield was 6% greater in the Bt plots.

I. INTRODUCTION:

European corn borer is a key pest of field corn in the Midwest. Feeding by ECB larvae cause stalk tunneling resulting in lodged plants, fallen ears, and reduced yield. Chemical control is available but is relatively expensive in relation to the potential yield loss and frequency of occurrence of ECB, thus is not widely used. Several seed companies have been developing ECB resistant corn varieties through incorporation of the gene that expresses the delta endotoxin produced by Bacillus thuringiensis, which is a natural insecticide. This study was designed to evaluate the incidence of ECB in þnon-Btþ and þBtþ corn.

II. HYBRIDS EVALUATED:

       1.  Non-Bt corn: NK N6800 (non-resistant to ECB)

       2.  Bt corn: NK X6534 CBR (ECB resistant)

III. PLOT DESIGN AND SAMPLING TECHNIQUE:

This study consisted of a non-replicated, side-by-side planting of non-Bt and Bt corn. Sixteen rows of each variety was planted for this evaluation. Ten plants each from three randomly selected rows were sampled at maturity. Stalks were split lengthwise live ECB larvae were counted, and cavities produced by ECB feeding were measured. Ten ears from each of five randomly selected rows were removed, shelled and the grain weighed to estimate yield.

IV. RESULTS AND DISCUSSION:

Results are summarized in Table 1. While ECB was found in the Bt isoline, the tunneling was very small in comparison to the non-Bt isoline. In addition, the tunneling in the Bt isoline was caused by very small (less 3rd instar) larvae that appeared to have died, while the tunneling in the non-Bt lines was caused by mature caterpillars that had exited the stalk as an adult moth. This isoline containing the gene appeared to have protected the plant from infestation by ECB. While yield was not statistically different, yield was 6% (about 10 bushels) greater numerically in the Bt isoline. If a yield increase of this magnitude could be obtained, the dollar returns in yield certainly justify the increased cost incurred by purchasing the seed.

Table 1.  Mean (+/- SEM) response of corn isolines to European corn borer infestation.

Variety     % Plants Infested   # ECB/10 Plants   Tunnel Length     Yield (bu/A)
                                                  /10 Plants (cm)                      
NK X6534    13.3 (+/- 3.3)          0.33          1.0 (+/- 0.35)   174.22 (+/- 4.34)
NK N6800    67 (+/- 6.6)            0.33          27.2 (+/- 4.38)  163.78 (+/- 6.81)

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