|Buntin, G. David -|
|Lee, R. Dewey -|
Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2011
Publication Date: July 21, 2011
Citation: Ni, X., Wilson, J.P., Buntin, G., Guo, B., Krakowsky, M.D., Lee, R., Cottrell, T.E., Scully, B.T., Huffaker, A., Schmelz, E.A. 2011. Spatial patterns of aflatoxin levels in relation to ear-feeding insect damage in pre-harvest corn. Toxins. 3(7):920-931. Interpretive Summary: Fungus-produced toxin, like aflatoxin, contamination in post harvest corn from warm temperate, subtropical, and tropical regions presents a serious health problem for human food, animal feed, and ethanol production. Aflatoxins are produced by a fungus, which threaten certain human food and animal feed sources growth under the warm environmental conditions. Reduction of aflatoxin contamination is a long-term goal for corn, peanut, and other crops in these regions. Reducing biotic and abiotic stresses and breeding for insect and aflatoxin resistance has been part of the integrated tactics for reducing aflatoxin contaminations in corn production. The roles of ear-feeding insects and their damage in aflatoxin contamination have been documented in recent decades. However, the roles of kernel-feeding insects in aflatoxin accumulation are still not clear. The current study is one of the first multiple-year studies utilizing high resolution grid-sampling technique throughout a field to assess the spatial patterns of maize weevil infestations and other ear-feeding insect damage in relation to aflatoxin contamination. The study shows a highly aggregated pattern of cob- and kernel-feeding insect infestations and damage, and aflatoxin contaminations, as well as a strong edge effect of both insect damage and aflatoxin levels. Aflatoxin levels were better correlated to the kernel-feeding maize weevils and kernel damage by stink bugs than to cob-feeding corn earworm damage. Although not empirically tested, these data suggest that researchers might consider testing practical prevention and/or management tactics for reducing both insect damage and aflatoxin contamination in further study. For example: 1) selective application of insecticides or fungicides to field perimeters, which may reduce both insect damage and aflatoxin contamination at the most susceptible field edges; 2) separate harvest of the perimeter and interior portions of a corn field thereby segregating grain by potential for aflatoxin infestation; and 3) selecting larger fields that are relatively square in shape to decrease the perimeter to area ratio of the field.
Technical Abstract: Key impediments to increased corn yield and quality in the southeastern US coastal plain region are damage by ear-feeding insects and aflatoxin contamination caused by infection of Aspergillus flavus. Key ear-feeding insects are corn earworm, Helicoverpa zea, fall armyworm, Spodoptera frugiperda, maize weevil, Sitophilus zeamais, and brown stink bug, Euschistus servus. In 2006 and 2007, aflatoxin contamination and insect damage were sampled before harvest in three 0.4-hectare corn fields using a grid sampling method. The feeding damage by each of ear/kernel-feeding insects (i.e., corn earworm/fall armyworm damage on the silk/cob, and discoloration of corn kernels by stink bugs), and maize weevil population were assessed at each grid point with five ears. The spatial distribution pattern of aflatoxin contamination was also assessed using the corn samples collected at each sampling point. Aflatoxin level was correlated to the number of maize weevils and stink bug-discolored kernels, but not closely correlated to either husk coverage or corn earworm damage. Contour maps of the maize weevil populations, stink bug-damaged kernels, and aflatoxin levels exhibited an aggregated distribution pattern with a strong edge effect on all three parameters. The separation of silk- and cob-feeding insects from kernel-feeding insects, as well as chewing (i.e., the corn earworm and maize weevil) and piercing-sucking insects (i.e., the stink bugs) and their damage in relation to aflatoxin accumulation is economically important. Both theoretic and applied ramifications of this study were discussed by proposing a hypothesis on the underlying mechanisms of the aggregated distribution patterns and strong edge effect of insect damage and aflatoxin contamination. Possible management tactics for aflatoxin reduction by proper management of kernel-feeding insects were also discussed. Future directions on basic and applied research related to aflatoxin contamination are also discussed.