Spatial Patterns of Aflatoxin Levels in Relation to Ear-Feeding Insect Damage in Pre-Harvest Corn

Xinzhi Ni,G David Buntin,R Dewey Lee,Baozhu Guo,Alisa Huffaker,Matthew D Krakowsky,Ted E Cottrell,Jeffrey P Wilson,Eric A Schmelz,Brian T Scully

doi:10.3390/toxins3070920

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, and by discussing possible management tactics for aflatoxin reduction by proper management of kernel-feeding insects. Future directions on basic and applied research related to aflatoxin contamination are also discussed.

Highlights

Aflatoxin contamination in post harvest corn presents a serious health problem for human food, animal feed, and ethanol feedstocks from warm temperate, subtropical, and tropical regions worldwide [1,2]
Data presented here showed that patterns of maize weevil infestation, percentage of stink bug-damaged kernels, and aflatoxin levels in the grain were distributed in aggregations throughout a field with a strong edge effect at pre-harvest
Among all aspects of the research related to aflatoxin reduction, host plant resistance to aflatoxin accumulation and breeding efforts are making significant progress, whereas quantifying the ecological interactions of both biotic and abiotic factors has been lagging behind

Summary

Introduction

Aflatoxin contamination in post harvest corn presents a serious health problem for human food, animal feed, and ethanol feedstocks from warm temperate, subtropical, and tropical regions worldwide [1,2]. A. parasiticus, which threaten certain human food and animal feed sources grown under the warm environmental conditions [3,4,5]. Reduction of aflatoxin contamination is a long-term goal for corn, peanut, and other crops in these regions. The roles of Lepidopteran pests [including corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), and fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae)] in aflatoxin contamination in corn have been documented in recent decades [7,8,9,10]. The role of kernel damage by maize weevil [Sitophilus zeamais

Results

Discussion

Conclusion