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Adult lesser grain borers. Link to photo information
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Getting a "Charge" From Bugs in Wheat

By Erin Peabody
May 21, 2007

How do you spot tiny insects that might be lurking inside grains bound for the kitchen table? Give them a minor jolt, according to an Agricultural Research Service (ARS) engineer.

Thomas Pearson, who works at the agency's Grain Marketing and Production Research Center, Manhattan, Kan., has found a novel and cost-effective way to detect the pesky insect larvae that occasionally use kernels of our favorite cereal grains as their homes.

Several agricultural researchers, including Pearson, are hard at work devising new and improved methods for helping inspectors screen our nation's grain supply. Why? Despite rigorous scrutiny of grain at flour mills and loading docks for overseas shipments, insects, in all their earthly abundance, remain persistent invaders of stored grains.

Especially hard to find are immature insects—tender pupae and larvae that metamorphose inside the nutrient-rich cocoon of a grain kernel until they're ready to emerge as adults.

Pearson's detection system relies on three parts: a roller system for crushing a sample of wheat, a voltage source for sending a charge through the sample, and a computer software program for measuring aspects of the sample's electrical conductance.

Kernels infested with larvae cause a noticeable spike in electrical conductivity readings. Such increases are likely due to the hidden larvae's moisture content.

For his study, Pearson intentionally infested batches of hard winter wheat and soft winter wheat with two of the grain industry's most insidious foes: the rice weevil and lesser grain borer. He allowed the contaminated samples to "incubate" for several weeks so that stowaway insects had a chance to multiply and grow, and so that their unnerving presence could be independently confirmed.

Pearson's specially adapted roller mill can impressively screen about 30,000 kernels—or one kilogram of grain—a minute, spotting 80 to 90 percent of those infested with insect larvae. The cost of the device is substantially less than other technologies for insect detection, including x-ray and near-infrared systems.

ARS is the U.S. Department of Agriculture's chief scientific research agency.