Insect Larval Activity on Developing Corn Ears and Subsequent Aflatoxin Contamination of Seed1

Abstract

Insect larvae that feed on developing corn kernels have been implicated in establishment of Aspergillus flavus Link ex Fr. infection and subsequent contamination of the seed with aflatoxin before harvest. The effect of environment on the association between A. flavus and 2 corn insects was examined on corn grown at diverse locations. Corn ears at Tifton, Ga., Ankeny, Iowa, and Portageville, Mo., were hand-infested with corn earworm, Heliothis zea (Boddie), and European corn borer, Ostrinia nubilalis (Hübner), and inoculated with A. flavus spores. Test corn was planted at different times to acquire varied maturity stages in ears during the growing season. Insects were collected from ears at staggered times after flowering and examined for A. flavus. The highest incidence of the fungus on corn insects was observed in Georgia samples (21.9%); Missouri insects provided an intermediate occurrence (13.7%); and the lowest fungal presence was found on insects from Iowa (7.3%). Infestation of ears with insects and introduction of fungal spores into the silk bundle increased levels of toxin in mature seeds, particularly in Georgia and Missouri corn. Ears exhibiting the greatest visual insect damage provided seed with the highest aflatoxin levels. The results provided compelling evidence for the role of corn insects in transferring A. flavus spores from the silk region of the ear into the region of developing kernels and subsequent formation of aflatoxin in seed. The extent of the fungal-insect association and related toxin production was influenced by regional factors.