Spatial and temporal patterns of insect damage and aflatoxin contamination in corn at pre-harvest

Ear-feeding insect damage and aflatoxin contamination are the key impediments to corn yield and quality under warm climatic conditions worldwide. A series of experiments have been conducted to examine the contribution of insect damage to aflatoxin contamination. To assess the spatial and temporal patterns, aflatoxin contamination and insect damage was sampled twice with a 4-wk interval before harvest in 2008 and 2009 using a grid-sampling method. The feeding damage by each of the 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 harvested corn samples from each sampling point. The aflatoxin level was not correlated to the number of maize weevils, but correlated to stink bug-discolored kernels in the corn fields in 2008, whereas the 2009 data showed the opposite. The maize weevil infestation, stink bug-damaged kernels, and aflatoxin levels also showed a clustered distribution pattern with a strong edge effect across the fields. The comparison of the results from the two-sampling dates showed that temporal pattern of aflatoxin levels was only changed in 2009, but not in 2008. The separation of silk- and cob-feeding from kernel-feeding insects and their damage in relation to aflatoxin accumulation and its management strategies will also be discussed.