Biotic and abiotic factors limiting efficacy of Bt corn in indirectly reducing mycotoxin levels in commercial fields.

Incidence of insect damage, and association of insect damage with mycotoxigenic corn ear molds and mycotoxins was examined in commercial fields of Bt and non-Bt hybrids of different backgrounds in Illinois in 1998 and 1999. Nearly 50% Helicoverpa zea (Boddie) infestation sometimes occurred in Bt hybrids that express high levels of the protein in silks and kernels. Damage by European corn borer, Ostrinia nubilalis Hübner, was uncommon, even in non-Bt ears. Levels of total fumonisins were generally less (15- to 1.8-fold) in Bt versus non-Bt hybrids at the same site, with some significant differences. There were several instances where there were no significant differences in fumonisin levels between low/no Bt kernel hybrids and Bt hybrids that produced high levels of the protein in the kernel and silk tissue. However, significant correlations were often noted between numbers of insect-damaged kernels and total fumonisin levels, especially in 1998, suggesting in these cases that reducing insect damage was still reducing fumonisin levels. There was variability between the correlation coefficient for numbers of insect damaged kernels and fumonisin levels at different sites for the same year, different hybrids at the same site, and the same hybrid for different years. Although reductions in fumonisins in Bt hybrids were more limited than reported in the past, planting the Bt hybrids still appears to be a useful method for indirectly reducing mycotoxins in corn ears.