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 mycotoxig enic, 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 hy brids that express high levels of the protein in silks and kernels. Damage by European corn borer, Ostrinia nubilalis Hubner, was uncommon, even in no n-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 differ ences. There were several instances where there were no significant differe nces in fumonisin levels between low/no Bt kernel hybrids and Bt hybrids th at produced high levels of the protein in the kernel and silk tissue. Howev er, significant correlations were often noted between numbers of insect-dam aged 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 differen t 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 us eful method for indirectly reducing mycotoxins in corn ears.